506 DEPENDENCE OF PLANT FORM ON SOIL AND CLIMATE. 



foots which have developed on muddy but not inundated ground displaj' three- 

 or five-cleft leaves whose segments are light green in colour, shiny, and almost 

 fleshy, and spread out flat. When these plants are grown under water the leaves 

 appear quite diflerent; they become divided into numerous thread-like or hair- 

 shaped segments which have a dark-green colour, and the polished surface has 

 entirely disappeared. 



The shade afibrded by stones, loose earth, undergrowth, and neighbouring 

 bushes and shrubs acts on growing stems, foliage-leaves, and flowers just in the 

 same way as the light-subduing layer of water. In a place near my country house 

 which was formerly used for storing wood and dry twigs, but which had remained 

 unused for a long time, the Creeping Thistle {Girsium arvense) had established itself 

 and formed an intricate growth. The crowded stems attained a height of SO cm. 

 at the time of flowering and fruit ripening. In the winter of 1885 wood was 

 again stored there in piles 150 cm. high. When, early in the following summer, 

 the new shoots of the Thistle began to spring up they were obliged to content 

 themselves with growing through the dark chinks between the blocks of wood. 

 Many were thus forced to bend and twist, and finally came against some insur- 

 mountable obstacle so that they dwindled in the crevices of the wood-stack without 

 ever reaching the light. Others again which were able to find a fairly straight 

 road through the crevices grew up until they reached the surface of the wood-heap, 

 thej^ then continued to grow 50 cm. higher and unfolded large foliage-leaves on 

 this upper portion. They also developed branches with flower-heads, and from 

 a distance it looked as if a group of Thistles had grown on the top of the wood- 

 stack. The stems had attained a height of 2 metres. The lower internodes were 

 twice as long as usual, the foliage-leaves which sprang from the stalk inside the 

 dark crevices were small, yellowish green, and the buds in their axils did not 

 develop. The Cow-berry (Vaccinium Vitis-Idcea) behaves similarly when its 

 shoots are obliged to grow up to the light through dead tree-trunks. Shoots which 

 force their way in the dark between the bark and the wood of the trunk may 

 reach the height of a metre, while neighbouring ones, springing directly from the 

 soil of the forest are only 15 cm. high. The shoots inside the bark have a reddish 

 colour, and they bear small pale scales instead of dark -green foliage-leaves. 



From the creeping stems of the White Clover (Trifolium repens) spring erect 

 petioles terminating in three leaflets, and an erect angular stem bearing a flower- 

 head. In sunn}^ places, especially where no neighbouring plants cast a shade, the 

 petioles reach a length of 8 cm., and the stem of 10 cm. But if dense bushes 

 overshade the Clover, the petiole and stem elongate until the leaflets and capitulum 

 they bear reach the light. Under these conditions petioles 28 cm. long have been 

 found, and stems attaining a height of 55 cm. An extraordinarj^ elongation also 

 occurs in the radical leaves of the Dandelion (Taraxacum oficmale) in places 

 where high Grasses and thick bushes shade the moist soil. In the open the leaves 

 reach 'i length of 20 cm., but in the shade they become twice or three times as 

 long. The lower part of the leaf lengthens most, the free end is comparatively 



