290 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



zomes. 



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

 may be 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 

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

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

 Stachys tuberifera and Siachys palustris, both of which have imderground rhi- 

 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 migh t arise. Under these 

 conditions rhizomes do develop, however, 

 from axiUary 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 darken- 

 ing, by surrounding the upper part of the 

 stem with an opaque box. {After VSchting.) 



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 

 a time and aerial rhizomes are produced. These experiments prove definitely 

 that tubers and rhizomes are really modified stems, in the sense of the plant 

 morphologists. 



In the examples described above, of the experimental production of aerial 

 tubers and rhizomes, the nutrient materials, being unable to accumulate in 



* VficMing, Hermann, Ueber eine abnorme Rhizom-Bildung. Bet. Zeitg. 47: S01-S07. 1889. 



