GENERAL MOBPHOLOGY OP THE PLANT 49 



indicates its nature as a kind of stem. This stem-like nature 

 of the tuber is also clearly proved by the practice commonly 



Fig, 75. 



Fig. 76. 



Fig. 77. 



Fig. 75. Corms of Crociis aativus. a, 6. The new corms, arising from c, the 



apex of the old or parent corm. Fig. 76. Vertical section of the former. 



The letters refer to the same pirts. 



adopted for propagating potatoes, the tuber being cut into pieces, 



each piece containing one or more buds. When these pieces 



are placed under favourable circumstances for development, the 



buds are at first nourished by the matter 



which surrounds them, and are thus enabled 



to put forth roots and obtain nourishment 



for themselves, and in this manner to form 



independent plants. The Potato {fig. 68) 



and Jerusalem Artichoke ( fig. 69) afford good 



illustrations of tubers. 



In certain plants, such as some epiphytic 

 Orchids, a portion of the sah-acrial stem 

 may be thickened, the thickening sometimes 

 being confined to one internode, sometimes 

 extending to more than one. This thickening, 

 which resembles a tuber, is often spoken of 

 as a, ]}seudohulh (fig. 33, b). 



c. The Bulb. — This is a shortened, usually 

 subterranean stem or branch, generally in 

 the form of a rounded or flattened plate or 

 disc (figs. 70-72, a), which bears on its sur- 

 face a number of fleshy scales or cataphyl- 

 lary leaves ; or it may be considered as a 

 subterranean bud of a scaly nature which 

 sends off roots or rootlets from below (fig. 72, i), and a flowering 

 stem upwards (fig. 70, x^, and figs. 71 and 72, d). The scales 



VOL. I. E 



Fig. 77. Oolchicum. 

 r. Roots or root- 

 lets. /. Leaf. a. 

 Shrivelled remains 

 of last year's corm 

 a'. Corm of the 

 present year. a'". 

 Commencement of 

 the corm of next 

 year. 



