THE STEM. 



15 



The superimposed rootstock of the Crocus presents a transition from the bulb to 

 the rootstock proper, for it may equally be regarded as a vertical rootstock or as a 

 series of superimposed bulbs. 



The roots of Orchis., which are both fibrous and tuberous, are classed with true 

 bulbs, differing from ordinary bulbs only in the swelling- of some of the root-fibres. 

 The two tubers are ovoid (fig. 43) or palmate (fig. 44), and are unequal; one (T 1) 

 is dark- coloured, wrinkled, flabby, and empty, and gives off the flowering stem ; the 



Ti 



Ta 



43. Orchis. Tuberous root. 



44. Orchis maculata. Palmate tuberous root. 



45. Orchis macnlata. 

 Palma.e tuberous root, cut vertically. 



other (T 2) is larger, whiter, and more succulent, often ending in well-developed 

 fibres (F), and bears a shoot (B 2), from the base of which grow fibrous roots. The 

 two tubers (fig. 45) are united above by a very short neck (P 1). This neck 

 connects the old tuber (T 1) with the new one (T 2), and from it the latter descends, 

 and a leafy shoot (B 2} ascends, which in the following year will bear a flowering 

 stem ; between this large shoot and 

 the old stem a vertical cut reveals 

 a third tiny shoot (B 3), developed 

 from the young tuber, and destined 

 to succeed it in the third year. 

 There are thus three generations in 

 the rootstock of an Orchis, each of 

 which requires two years for its 

 perfect development, and dies at 

 the end of the third, after having 

 flowered ; and the same may be seen 

 in Carex, Crocus, and ordinary bulbs. 

 The term tubers (tubera, tuber- 

 cula) has been given to the dilated 

 extremities of underground roots, 

 usually containing starch. These swellings bear rudimentary leaves, in the axils 

 of which are eyes or buds, which develop into steins (Jerusalem Artichoke ; Potato, 

 fig. 46). The conversion of shoots into tubers can be encouraged by earthing- 



46. Potato. Subterranean branches bearing tubercles. 



