DEVELOPMENT AND REPRODUCTION 



329 



ment of organic materials through the stem occurs mainly in the direction oppo- 

 site to that in which it usually occurs; these substances here move from the 

 leaves below to the tubers above. 



Vochting 1 showed that tuber-formation in the potato is dependent also upon 

 many other external conditions, besides those here mentioned. Aerial tubers 

 maybe similarly produced on other plants that usually bear subterranean tubers. 

 Because of their position in the soil, rhizomes or root-stocks, which are of 

 frequent occurrence in plants, are often thought to be roots, but they are really 

 subterranean stems, for they possess dormant buds that may develop later 

 into aerial branches. Vochting 2 has shown experimentally that this is true for 

 Stachys tuberifera and Stachys palustris, both of which have underground rhi- 

 zomes. Aerial rhizomes may be obtained with these plants by the same treat- 

 ment as was employed to bring about the 

 development of aerial tubers in the potato. 

 If all the buds are removed from the basal 

 portion of a cut leafy branch and this por- 

 tion of the stem is then placed in soil, 

 roots develop but no under-ground rhi- 

 zomes are formed, there being no buds on 

 the underground portion of the stem, from 

 which rhizomes might arise. Under these 

 conditions rhizomes do develop, however, 

 from axillary buds on the upper portion 

 of the stem, thus replacing the usual 



Fig. 167. — Development of terminal buds 

 into aerial tubers as a result of darkening, 

 by surrounding the upper part of the stem 

 with an opaque box. {After Vochting.) 



Fig. 168. — Transformation of a leafy branch 

 of Stachys tuberifera into aerial rhizomes. 

 (After Vochting.) 



lateral branches (Fig. 168). Aerial rhizomes may be obtained in another way, 

 in the plants employed by Vochting (especially in Stachys palustris) . If normally 

 developed plants, with subterranean rhizomes, are brought indoors in late 

 autumn, when they are full-grown and are about to die, growth is resumed after 



1 Vochting, Hermann, Ueber die Keimung der Kartoffelknollen. Experimentelle Untersuchungen. 

 Bot. Zeitg. 6o 7 : 87-114. 1902. 



2 Vochting, Hermann, Ueber eine abnorme Rhizom-Bildung. Bot. Zeitg. 47: 501-507. 2889. 



