This problem of the shape of leaves certainly seems to me a most important one; and yet it has hardly been even recognised by our scientific pastors9 and masters. At best, Mr. Herbert Spencer devotes to it a passing short chapter, or Mr. Darwin a stray sentence. The practice of classifying plants mainly by means of their flowers has given the flower a wholly factitious and overwrought importance. Besides, flowers are so pretty, and we cultivate them so largely, with little regard to the leaves, that they have come to usurp10 almost the entire interest of botanists11 and horticulturists alike. Darwinism itself has only heightened this exclusive interest by calling attention to the reciprocal relations which exist between the honey-bearing blossom and the fertilising insect, the bright-coloured petals12 and the myriad13 facets14 of the butterfly's eye. Yet the leaf is after all the real plant, and the flower is but a sort of afterthought, an embryo15 colony set apart for the propagation of like plants in future. Each leaf is in truth a separate individual organism, united with many others into a compound community, but possessing in full its own mouths and digestive organs, and carrying on its own life to a great extent independently of the rest. It may die without detriment16 to them; it may be lopped off with a few others as a cutting, and it continues its life-cycle quite unconcerned. An oak tree in full foliage is a magnificent group of such separate individuals—a whole nation in miniature: it may be compared to a branched coral polypedom covered with a thousand little insect workers, while each leaf answers rather to the separate polypes themselves. The leaves are even capable of producing new individuals by what they contribute to the buds on every branch; and the seeds which the tree as a whole produces are to be looked upon rather as the founders17 of fresh colonies, like the swarms18 of bees, than as fresh individuals alone. Every plant community, in short, both adds new members to its own commonwealth19, and sends off totally distinct germs to form new commonwealths20 elsewhere. Thus the leaf is, in truth, the central reality of the whole plant, while the flower exists only for the sake of sending out a shipload of young emigrants21 every now and then to try their fortunes in some unknown soil.
The whole life-business of a leaf is, of course, to eat and grow, just as these same functions form the whole life-business of a caterpillar22 or a tadpole23. But the way a plant eats, we all know, is by taking carbon and hydrogen from air and water under the influence of sunlight, and building them up into appropriate compounds in its own body. Certain little green worms or convoluta have the same habit, and live for the most part cheaply off sunlight, making starch24 out of carbonic acid and water by means of their enclosed chlorophyll, exactly as if they were leaves. Now, as this is what a leaf has to do, its form will almost entirely25 depend upon the way it is affected26 by sunlight and the elements around it—except, indeed, in so far as it may be called upon to perform other functions, such as those of defence or defiance27. This crowfoot is a good example of the results produced by such agents. Its lower leaves, which grow under water, are minutely subdivided28 into little branching lance-like segments; while its upper ones, which raise their heads above the surface, are broad and united, like the common crowfoot type. How am I to account for these peculiarities29? I fancy somehow thus:—
Plants which live habitually30 under water almost always have thin, long, pointed31 leaves, often thread-like or mere32 waving filaments33. The reason for this is plain enough. Gases are not very abundant in water, as it only holds in solution a limited quantity of oxygen and carbonic acid. Both of these the plant needs, though in varying quantities: the carbon to build up its starch, and the oxygen to use up in its growth. Accordingly, broad and large leaves would starve under water: there is not material enough diffused34 through it for them to make a living from. But small, long, waving leaves which can move up and down in the stream would manage to catch almost every passing particle of gaseous35 matter, and to utilise it under the influence of sunlight. Hence all plants which live in fresh water, and especially all plants of higher rank, have necessarily acquired such a type of leaf. It is the only form in which growth can possibly take place under their circumstances. Of course, however, the particular pattern of leaf depends largely upon the ancestral form. Thus this crowfoot, even in its submerged leaves, preserves the general arrangement of ribs36 and leaflets common to the whole buttercup tribe. For the crowfoot family is a large and eminently37 adaptable38 race. Some of them are larkspurs and similar queerly-shaped blossoms; others are columbines which hang their complicated bells on dry and rocky hillsides; but the larger part are buttercups or marsh39 marigolds which have simple cup-shaped flowers, and mostly frequent low and marshy40 ground. One of these typical crowfoots under stress of circumstances—inundation, or the like—took once upon a time to living pretty permanently41 in the water. As its native meadows grew deeper and deeper in flood it managed from year to year to assume a more nautical42 life. So, while its leaf necessarily remained in general structure a true crowfoot leaf, it was naturally compelled to split itself up into thinner and narrower segments, each of which grew out in the direction where it could find most stray carbon atoms, and most sunlight, without interference from its neighbours. This, I take it, was the origin of the much-divided lower leaves.
But a crowfoot could never live permanently under water. Seaweeds and their like, which propagate by a kind of spores43, may remain below the surface for ever; but flowering plants for the most part must come up to the open air to blossom. The sea-weeds are in the same position as fish, originally developed in the water and wholly adapted to it, whereas flowering plants are rather analogous44 to seals and whales, air-breathing creatures, whose ancestors lived on land, and who can themselves manage an aquatic45 existence only by frequent visits to the surface. So some flowering water-plants actually detach their male blossoms altogether, and let them float loose on the top of the water; while they send up their female flowers by means of a spiral coil, and draw them down again as soon as the wind or the fertilising insects have carried the pollen46 to its proper receptacle, so as to ripen47 their seeds at leisure beneath the pond. Similarly, you may see the arrowhead and the water-lilies sending up their buds to open freely in the air, or loll at ease upon the surface of the stream. Thus the crowfoot, too, cannot blossom to any purpose below the water; and as such among its ancestors as at first tried to do so must of course have failed in producing any seed, they and their kind have died out for ever; while only those lucky individuals whose chance lot it was to grow a little taller and weedier than the rest, and so overtop the stream, have handed down their race to our own time.
But as soon as the crowfoot finds itself above the level of the river, all the causes which made its leaf like those of other aquatic plants have ceased to operate. The new leaves which sprout48 in the air meet with abundance of carbon and sunlight on every side; and we know that plants grow fast just in proportion to the supply of carbon. They have pushed their way into an unoccupied field, and they may thrive apace without let or hindrance49. So, instead of splitting up into little lance-like leaflets, they loll on the surface, and spread out broader and fuller, like the rest of their race. The leaf becomes at once a broad type of crowfoot leaf. Even the ends of the submerged leaves, when any fall of the water in time of drought raises them above the level, have a tendency (as I have often noticed) to grow broader and fatter, with increased facilities for food; but when the whole leaf rises from the first to the top the inherited family instinct finds full play for its genius, and the blades fill out as naturally as well-bred pigs. The two types of leaf remind one much of gills and lungs respectively.
But above water, as below it, the crowfoot remains50 in principle a crowfoot still. The traditions of its race, acquired in damp marshy meadows, not actually under water, cling to it yet in spite of every change. Born river and pond plants which rise to the surface, like the water-lily or the duck-weed, have broad floating leaves that contrast strongly with the waving filaments of wholly submerged species. They can find plenty of food everywhere, and as the sunlight falls flat upon them, they may as well spread out flat to catch the sunlight. No other elbowing plants overtop them and appropriate the rays, so compelling them to run up a useless waste of stem in order to pocket their fair share of the golden flood. Moreover, they thus save the needless expense of a stout51 leaf-stalk, as the water supports their lolling leaves and blossoms; while the broad shade which they cast on the bottom below prevents the undue52 competition of other species. But the crowfoot, being by descent a kind of buttercup, has taken to the water for a few hundred generations only, while the water-lily's ancestors have been to the manner born for millions of years; and therefore it happens that the crowfoot is at heart but a meadow buttercup still. One glance at its simple little flower will show you that in a moment.
点击
收听单词发音
收听单词发音 |
1
varied
|
|
| adj.多样的，多变化的 | |
参考例句： |
|
|
|
|
2
foliage
|
|
| n.叶子，树叶，簇叶 | |
参考例句： |
|
|
|
|
3
spikes
|
|
| n.穗( spike的名词复数 )；跑鞋；（防滑）鞋钉；尖状物v.加烈酒于( spike的第三人称单数 )；偷偷地给某人的饮料加入（更多）酒精（ 或药物）；把尖状物钉入；打乱某人的计划 | |
参考例句： |
|
|
|
|
4
watery
|
|
| adj.有水的，水汪汪的；湿的，湿润的 | |
参考例句： |
|
|
|
|
5
dangling
|
|
| 悬吊着( dangle的现在分词 )； 摆动不定； 用某事物诱惑…； 吊胃口 | |
参考例句： |
|
|
|
|
6
trout
|
|
| n.鳟鱼；鲑鱼(属) | |
参考例句： |
|
|
|
|
7
cleft
|
|
| n.裂缝；adj.裂开的 | |
参考例句： |
|
|
|
|
8
scant
|
|
| adj.不充分的，不足的；v.减缩，限制，忽略 | |
参考例句： |
|
|
|
|
9
pastors
|
|
| n.（基督教的）牧师( pastor的名词复数 ) | |
参考例句： |
|
|
|
|
10
usurp
|
|
| vt.篡夺，霸占；vi.篡位 | |
参考例句： |
|
|
|
|
11
botanists
|
|
| n.植物学家，研究植物的人( botanist的名词复数 ) | |
参考例句： |
|
|
|
|
12
petals
|
|
| n.花瓣( petal的名词复数 ) | |
参考例句： |
|
|
|
|
13
myriad
|
|
| adj.无数的；n.无数，极大数量 | |
参考例句： |
|
|
|
|
14
facets
|
|
| n.（宝石或首饰的）小平面( facet的名词复数 )；（事物的）面；方面 | |
参考例句： |
|
|
|
|
15
embryo
|
|
| n.胚胎，萌芽的事物 | |
参考例句： |
|
|
|
|
16
detriment
|
|
| n.损害；损害物，造成损害的根源 | |
参考例句： |
|
|
|
|
17
founders
|
|
| n.创始人( founder的名词复数 ) | |
参考例句： |
|
|
|
|
18
swarms
|
|
| 蜂群，一大群( swarm的名词复数 ) | |
参考例句： |
|
|
|
|
19
commonwealth
|
|
| n.共和国，联邦，共同体 | |
参考例句： |
|
|
|
|
20
commonwealths
|
|
| n.共和国( commonwealth的名词复数 )；联邦；团体；协会 | |
参考例句： |
|
|
|
|
|
21
emigrants
|
|
| n.（从本国移往他国的）移民( emigrant的名词复数 ) | |
参考例句： |
|
|
|
|
22
caterpillar
|
|
| n.毛虫，蝴蝶的幼虫 | |
参考例句： |
|
|
|
|
23
tadpole
|
|
| n.[动]蝌蚪 | |
参考例句： |
|
|
|
|
24
starch
|
|
| n.淀粉；vt.给...上浆 | |
参考例句： |
|
|
|
|
25
entirely
|
|
| ad.全部地，完整地；完全地，彻底地 | |
参考例句： |
|
|
|
|
26
affected
|
|
| adj.不自然的，假装的 | |
参考例句： |
|
|
|
|
27
defiance
|
|
| n.挑战，挑衅，蔑视，违抗 | |
参考例句： |
|
|
|
|
28
subdivided
|
|
| 再分，细分( subdivide的过去式和过去分词 ) | |
参考例句： |
|
|
|
|
29
peculiarities
|
|
| n. 特质, 特性, 怪癖, 古怪 | |
参考例句： |
|
|
|
|
30
habitually
|
|
| ad.习惯地，通常地 | |
参考例句： |
|
|
|
|
31
pointed
|
|
| adj.尖的，直截了当的 | |
参考例句： |
|
|
|
|
32
mere
|
|
| adj.纯粹的；仅仅，只不过 | |
参考例句： |
|
|
|
|
33
filaments
|
|
| n.（电灯泡的）灯丝( filament的名词复数 )；丝极；细丝；丝状物 | |
参考例句： |
|
|
|
|
34
diffused
|
|
| 散布的，普及的，扩散的 | |
参考例句： |
|
|
|
|
35
gaseous
|
|
| adj.气体的，气态的 | |
参考例句： |
|
|
|
|
36
ribs
|
|
| n.肋骨( rib的名词复数 )；（船或屋顶等的）肋拱；肋骨状的东西；（织物的）凸条花纹 | |
参考例句： |
|
|
|
|
37
eminently
|
|
| adv.突出地；显著地；不寻常地 | |
参考例句： |
|
|
|
|
38
adaptable
|
|
| adj.能适应的，适应性强的，可改编的 | |
参考例句： |
|
|
|
|
39
marsh
|
|
| n.沼泽，湿地 | |
参考例句： |
|
|
|
|
40
marshy
|
|
| adj.沼泽的 | |
参考例句： |
|
|
|
|
41
permanently
|
|
| adv.永恒地，永久地，固定不变地 | |
参考例句： |
|
|
|
|
42
nautical
|
|
| adj.海上的，航海的，船员的 | |
参考例句： |
|
|
|
|
43
spores
|
|
| n.（细菌、苔藓、蕨类植物）孢子( spore的名词复数 )v.（细菌、苔藓、蕨类植物）孢子( spore的第三人称单数 ) | |
参考例句： |
|
|
|
|
44
analogous
|
|
| adj.相似的；类似的 | |
参考例句： |
|
|
|
|
45
aquatic
|
|
| adj.水生的，水栖的 | |
参考例句： |
|
|
|
|
46
pollen
|
|
| n.[植]花粉 | |
参考例句： |
|
|
|
|
47
ripen
|
|
| vt.使成熟；vi.成熟 | |
参考例句： |
|
|
|
|
48
sprout
|
|
| n.芽，萌芽；vt.使发芽，摘去芽；vi.长芽，抽条 | |
参考例句： |
|
|
|
|
49
hindrance
|
|
| n.妨碍，障碍 | |
参考例句： |
|
|
|
|
50
remains
|
|
| n.剩余物，残留物；遗体，遗迹 | |
参考例句： |
|
|
|
|
52
undue
|
|
| adj.过分的；不适当的；未到期的 | |
参考例句： |
|
|
|
| 欢迎访问英文小说网 |