[Chap. XXXV 



VEGETATIVE MULTIPLICATION 



411 



growing seasons. Bulbs or bulblets may develop from buds on aerial 

 stems also, as in certain varieties of lily and onion (Fig. 186B). Some 

 water plants have bulblike compact winter buds which become sepa- 

 rated by the death of the older parts of the stem. These buds float about 

 in the water or settle to the bottom of the lake or pond. In the following 

 spring roots and shoots develop from them. 



Gardeners do not usually transplant bulbs and corms until after the 

 tops of the plants have died. These propagules may also be stored 

 and shipped, but the temperatures to which they are exposed may greatly 

 affect the subsequent growth of plants from them. Improper storage 

 temperatures are sometimes the cause of worthless plants. Diseases 

 caused by viruses which spread throughout the plants may also become 

 a menace to the bulb industry. Intelligent inspection of the growing 

 plants and of the bulbs placed on the market, accompanied by reason- 

 able laws and their enforcement, is the only means of protecting the 

 purchaser of bulbs. 



The buds of bulbs and of corms have definite periods of domiancy, and 

 the best plants are not obtained unless the donuant period is passed 



Fig. 187. Rhizome of Eryngiiim with distinct annual segments and branches, seen 

 from the side, and from below. From H. S. Jurica. 



under suitable conditions. Tubers, corms, and bulbs, like rhizomes, have 

 fairly specific levels of growth in the soil. If they are planted below or 

 above this level, the new ones are formed a little nearer to it each suc- 

 ceeding year. This phenomenon appears to be related primarily to light. 

 Offsets and basal sprouts. Many plants, both herbaceous and woody, 

 multiply vegetatively by offsets, sprouts, and tillers, all of which have a 

 similar origin from lateral buds near the base of the stem (Figs. 187 and 

 188). This process occurs annually in some species of plants, such as 

 rose, sedum, aster, and goldenrod; but in shrubs and trees the lateral 



