414 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 



It was not witliout reason that in each separate instance hitherto described, 

 emphasis has been laid on the fact that the foliage-leaves in question were situated 

 on erect stems, and this must again be particularly pointed out here. The con- 

 ditions on horizontal branches are entirely different, and what is suitable for 

 one is not always fitted to the other. It is easy to make this evident. It is 

 only needful to bend down an erect leafy maple-branch until it becomes horizontal, 

 and it will immediately be seen that the surfaces of the leaves on tlie branch 

 assume a position and direction very different from their previous attitude. The 

 narrow side, instead of the broad side as previously, is directed towards the 

 incident light, and the leaves now stand above one another which formerly stood 

 •opposite at the same height from the ground. If the arrangement of the foliage- 

 leaves on the erect branch was previously suitable and beneficial, the contrary 

 is now the case. Such alterations in the position of the foliage-leaves or shoots 

 and branches of plants, however, occur not only by way of exception, but very 

 frequently. It signifies the less that strong winds bend and incline the leaf- 

 stalks and twigs, since this alteration of position is, as a rule, only of short dura- 

 tion, and when the storm is past, the former position is again taken up. The 

 pressure which snow exerts on plants in regions where in winter the fall is heavy, 

 is, indeed, of more importance, and can produce alterations in the position of the 

 twigs and branches which are of longer duration. But most important of all is 

 the fact that perennial plants add a new portion to the end of their shoots every 

 year, that they always develop each year new sprouts above those already existing, 

 and not only at the apex, but also from buds which arise laterally on the branches. 

 Let us observe a young maple whose topmost branch terminates in three buds. 

 Twigs issue from the three buds with the renewal of activity in the spring; the 

 central bud grows directly upwards, the two lateral rise obliquely; all three are 

 thickly leaved, and the foliage of the three twigs covers over and shades three, 

 four, perhaps ten times as large a space as the pair of leaves from whose base 

 the buds had developed in the pi-evious summer. 



Now, above the centre of the maple as it was in the previous year, what 

 may be termed a new richly-leaved and thickly overshadowing little maple-tree 

 grows up. That mutual consideration, which is otherwise observed by members 

 of the same plant, and which was described earlier, here ceases. The leaves of 

 the topmost shoot are, of course, so arranged that no mutual injury is done; 

 but very little attention appears to be paid to the leaves below, as little perhaps 

 as to the lower grasses and herbs which grow under the maple-tree on the 

 ground. 



But what are the branches to do which spring from the buds in the centre 

 of the maple-tree under consideration? If they take the same direction as the 

 branches at the extreme summit, they will come into the area of the dark shadows 

 thrown by the numerous broad leaves of the top branches. They are, therefore, 

 compelled to take up another direction if their leaves are not to perish from 

 want of light. And, as a matter of fact, this is what they do. They arrange 



