77 371 



lateral shoots (more or less connected with the basis of the same), and often, also, buds are 

 rapidly formed from the axils of the lowest leaves on the lateral shoots. For examples see 

 fii". 1, 4, 6, 8, 10, 12, 16, 22, 37, 41, 42. 



Of these basal shoots, some develo])e into aerial shoots, others more often to runners. 

 In Saiiunaria, for instance (Hj<. 10), Ilomketnia ilij». 12 runners are not formed at once, but are 

 evidently delayed until, by the contraction of the primary root or otherwise, the buds have 

 come down into the ground. In other species, runners grow out at once, and make their way 

 down into the ground. 



In some species, the cotyledon is hypogæic, and the runners are at once hypogæic, but 

 may nevertheless be seen to grow more or less obliquely down (fig. 21); it is probably the 

 force of gravity which forces them down until they have reached a depth determined by the 

 nature of the soil. Sjjccies with hyj^ogæic cotyledon are mentioned on p. 357. 



Particularly interesting is Phraqmilcs, the seedling of which will in the course of one 

 summer develope several generations of runners; each successive generation seeks farther 

 down, and becomes stronger then its predecessor, being evidently nourished by the older 

 aerial shoots. So also with Scirpus marilimus iWahming 1881; lig. 10 and 17) and S. Taber- 

 nœnwnlani (Warming 1909; fig. 117, 116). 



Epigæic cotyledons. Fig. 1, 3, 4, 6, 8, 9, 14, 16, 20, 21, 22, 27, 37, 38, 41, 42 show how 

 shoots grow out from the axils of the cotyledons or those of other leaves, obliquely 

 down into the earth. The question as to the part played by geotropy and heliotro|)y in these 

 movements must be determined l)y experiment. That direct light can force earth-stems to 

 move down into the earth has been shown experimentally by Stahl, Goebel and others. And 

 the point is further apparent from the fact that earth-stems which have grown out from the 

 banks of ponds into the water may be seen to turn sharply downwards (Warming 1897, lig. 12, 

 Cladinm mariscus; 1899 fig. 6, Scirpus lacustris; Raunkiær 1907, fig. 71—73). 



Soil level. Royer maintained (1870) that there was a certain "loi de niveau" or law of 

 level for each species; i.e. a definite soil level or normal depth, differing, however, according 

 to external conditions; cf also Woodhead (1906). I have here (p. 359) collected a quantity 

 of data concerning the depth at which the earth stems (of various types) may be found in 

 dilferent species. Speaking generally, the rule is that weak, hypogæic stems such as the 

 runners of Asperiila and Adoxa moschatellina, only go down to a slight depth. Species which 

 can be found at the surface of the earth and among the fallen leaves in forest ground, pene- 

 trating down only to some few centimetres' depth, are mentioned under 1) on p. 359. Under 

 2) are noted species whose earth-stems may be founil between 2— 4 cm down. Under 3, some 

 which are found at 4-10 cm depth. Those under 4) go down to 10-15 (-20) cm. Under 5) 

 are mentioned some few species which go still deeper. Many species may be found at 

 greatly varying depths, as has also been noted by P. E. Müller. The result of my investiga- 

 tions is, that it is extremely difficult to determine the normal soil level by investigations in a 

 state of nature. Many difierent factors may exert a modifying influence: the physical con- 

 ditions of the soil, the quantity and character of the air therein contained, acid or alkaline 

 nature of the ground, moisture, heat, amount of nutritive matter; furthermore, the season of 

 the year may count for someting, as especially also the age of the plant and its position in 

 regard to competition with other species. Finally, there are purely accidental circumstances 

 which have to be reckoned with, as for instance where earth or leaves are deposited by 

 earthworms (P. E. Müller) or by wind or water above the soil in which the stem is found, 

 or where the same are carried away by the rain. The only certain method of ascertaining 

 the normal soil level answering to given external conditions is that adopted by Rimbach, viz. 

 the experimental. 



Alteration of soil level. Rover saw that plants were able to alter the soil level of 

 tlieir earth stems, ascending or descending in accordance with changing conditions. There 

 are various ways in which this alteration can be eflected. When an orthotroi)ic stem has 

 got too deep down into the earth, it will be able to ascend simply by etiolation (figures. 

 for instance, in Raunki.kr 1905 fig. 13. 14. 15|. Plagiotropic stems, on finding themselves too 



