504 DEPENDENCE OF PLAXT FORM OX SOIL AND CLIMATE. 



of streams with a mean temperature of 10'2 ° C, but they also flourish in a stream 

 above the tree-line, at a height of 1921 metres above the sea-level, known as the 

 " Kreuzbrunnen ". Comparing plants of the same species growing under the 

 influence of these difierent temperatures, the following differences are to be noted: — 

 Plants of Veronica Beccabunga growing in spring water at a temperature of 

 10-2" C. were 20-50 cm. high, and displaj'ed 4-6 intemodes between the bottom 

 in which they were rooted and the level of the first inflorescencea The intemodes 

 of the stem were 60-120 mm. long and 5 mm. thick; the leaves springing from 

 the middle of the plant were 40-60 mm. long, 20-25 mm. broad, and each of the 

 flower racemes had 12-16 flowers. Plants growing in the spring water at a 

 temperature of 4'2° C. were 10-15 cm. high with 4-6 intemodes between the 

 ground and the level of the first inflorescences. The intemodes were 15-30 mm. 

 long and 10-12 mm. thick, and each inflorescence had 12-16 flowers. Cardamine 

 amara, Myosotis jMlustr'is, and Pedicularis palustris behaved similarly. There 

 seemed to be no alteration in the form of the leaves and flowers; the corollas 

 assumed a rather deeper tint in the Kreuzbrunnen; Myosotis pahistris, which 

 was 20 cm. high at the foot of the Patscherkofel, was 4-5 cm. high in the Kreuz- 

 brunnen, and closely resembled the Eritrichiv^m nanum of the Southern Alps 

 in the deep blue of its corollas. Cardamine amara, in the same cold spring, in 

 addition to the shortening of its intemodes and diminution of its foliage - leaves, 

 displayed a red colour on the outside of its white petals which was not present 

 in plants at lower levels. 



The powerful influence of light on the development of plants was discussed at 

 vol. i. p. 371. The question now before us is how far bright and subdued light are 

 able to alter the size, form, and colour of plants. The following is a general review 

 of what has been ascertained in the matter from experiments and direct observa- 

 tion of nature. When plants of a species develop in subdued light they always 

 have higher stems and longer leaves than when grown in bright light, provided, 

 of course, that the conditions of moisture and temperature have been as far as 

 possible identical. This diflerence is especially noticeable in comparing two plants 

 of a species, one of which has developed in the dim light of a greenhouse in the 

 short days of winter, the other in an unshaded place in the open country during 

 the summer when the light lasts for 16-17 hours every day. The former has a 

 lank thin stem, delicate yellowish-green leaves, and either none of its flowers 

 unfold or else they have a weak appearance and their corollas are pale and flaccid. 

 The illuminated plant has, on the other hand, a compact vigorous stem, dark green 

 leaves, and unfolds a multitude of bright-hued flowers. One only of the large 

 number of experiments which have been performed for the purpose of detennining 

 this matter definitely will be mentioned here — one indeed which shows how far 

 the form of the flowers also may be aflfected. Seeds of a biennial Saxifrage, 

 Saxifraga controversa, which were sown in several flower-pots filled with similar 

 soil, produced numerous young plants. A pot with six of these j'oung plants 

 was taken in the autumn into the hot-house; another, likewise containing 



