BULBS. PERENNATION 265 



one ; the bulbous buttercup {Ranunculus bulbosus) ; 

 common in dry pastures ; and Cyclamen. 



Bulbs. — The Ufe history of a plant which perennates 

 by means of iulbs is very similar in general features 

 to that of the corm-forming plants, the distinction being 

 that in the bulb the store of food is contained in the 

 scale leaves {iulh scales) of the winter shoot, the stem 

 being represented by a disc at the base of the bulb. 

 On this are inserted the outer membranous brown 

 protective scales, and the massive bulb scales which 

 form the greater part of the body of the bulb. 



In the Tulip, which is a suitable type for study, 

 there is however another difference. The aerial flowering 

 shoot is produced from the terminal bud of the bulb, 

 not, as in Crocus, from axillary buds. The new bulbs 

 are formed, not by the swelling of part of the aerial 

 shoot, but by the formation of buds in the axils of the 

 bulb scales. These buds gradually swell during the 

 growing season, as the old bulb scales become emptied, 

 and thus produce the new bulbs inside the old one. 

 It is even more important to dig up and remove tulip 

 bulbs from the soil at the end of the growing season 

 if the crop is to be maintained. 



Some bulb-forming plants (onions, lilies, etc.) also 

 produce under certain conditions small bulbs called 

 bulbils in place of all or some of the flowers. These 

 become detached, fall to the ground, and in suitable 

 soil strike root and reproduce the plant. 



Perennation, Multiplication and Spreading. — The 

 types of more or less specialised underground shoots 

 described — rhizomes, tubers, corms and bulbs — all serve 

 to carry the plant on in the vegetative form from one 

 growing season to the next, for they can exist unharmed 

 in a dormant condition in the soil through the winter, 



