SPECIAL FORMS. 61 



adventitious buds. Sweet potatoes (55), although equally 

 roots, do produce adventitious buds, especially from near the 

 upper end. The somewhat similar tubercles or tumefied roots 

 of certain Orchises and other plants of the same tribe, 1 definite 

 in number and shape, and sometimes imitating a corm, are 

 charged with a bud at the upper end, near their origin. Ap- 

 parently, the origin is a bud from the base of the parent 

 stem, which bud directly forms a tumefied short root from its 

 very base. 2 



118. A Corm (Cormus) is to be compared on the one hand 

 with a short rootstock or tuber, on the other with a bulb. It 

 is a subterranean fleslr^ stem, of rounded or depressed figure 

 and solid texture. Some of its buds grow into new corms, and 

 these, upon the death of or separation from the parent, become 

 new individuals : some develop above ground 

 the vegetation and the blossoms of the season. 

 A good type of corm is that of Cyclamen 

 (Fig. ,109), in which the very base of the 

 seedling stem grows fleslrv, and widens from 

 year to year, but hardly at all lengthens, and 

 so becomes far broader than high, or de- 

 pressed. As the main bulk belongs to the 109 

 first internode, or caulicle, the buds from which the yearly 

 growths of leaves and flower-stalks spring are at the centre of 

 the summit or upper surface, the roots 

 from the low r er, and the sides seldom pro- 

 duce any buds. The corm of Indian 

 Turnip (Arisaema triphyllum, Fig. 110) 

 is somewhat similar, but it sends up a 

 single stout stem, and the roots spring' 

 from around the base of this. These are 

 completely naked corms. 



119. But in Crocus (Fig. Ill, 112), Colchicum (Fig. 117), \ 

 Gladiolus, and the like, the sheathing bases of one or two leaves 

 enclose the corm with a membranous- scaly coat, giving it exactly 

 the appearance externally of a coated bulb. Such have been not 

 inappropriately named solid bulbs. In common parlance, they 

 will doubtless continue to be called bulbs, and even in popular 



1 Not, however, such as those of Aplectrum, Tipularia, etc., which are 

 genuine corms or tubers. 



3 Irmisch, Beitr. Biol. & Morphol. Orchid. 1853, fide Duchartre, lem. 

 Bot. 278. 



FIG. 109. Depressed corm of Cyclamen. 



FIG. 110. Corm of Indian Turnip, Arisaema triphyllum. 



