676 



ECOLOGY 



Land plants with little capacity for vegetative reproduction. — Many herbs with 

 persistent primary roots {e.g. dock, dandelion, vervain) die down to the ground in 

 autumn, appearing essentially stemless in winter. In reality there is a short thick 

 stem which elongates and enlarges slightly each year; at first only one bud is formed, 

 growing into a single leafy shoot, but, as the size increases, a number of buds are 



formed, growing into several leafy shoots. 

 Such a perennial stem is known as 

 multicipital (figs. 994-996, 716, 717). 

 Plants with multicipital stems do not 

 migrate, and vegetative reproduction is 

 very hmited, on account of the lack of 

 lateral ground stems with adventitious 

 roots; new stem increments are as de- 

 pendent as the old upon the persistent 

 primary root. Annual and biennial 

 herbs, many shrubs, and most trees have 

 persistent primary roots and are without 

 lateral ground stems bearing adventitious 

 roots ; like multicipital herbs, they have 

 little or no capacity for vegetative repro- 

 duction. While some trees exhibit propa- 

 gation by roots (p. 505), others (as the 

 linden and the redwood) produce suckers 

 at the base, thus resembling multicipital 

 herbs except in the persistence of the 

 aerial stems; basal shoots of this sort, 

 however, are of little reproductive sig- 

 nificance. In various trees and shrubs, 

 especially the willows, cuttings placed in 

 the soil develop into new plants; repro- 

 duction of this kind is rare in nature, 

 though employed artificially in many 

 plants. Of all the common trees the 

 conifers have the least capacity for vege- 

 tative reproduction, but a fallen Torreya 

 tree develops adventitious roots and erect 

 shoots along the trunk almost as readily 

 as do the willows. 



Fig. 993. — A plant of the dwarf ginseng 

 (Panax trifolium), showing a corm or solid 

 bulb (c) ; note the whorl of three palmately 

 compound leaves and the umbel of pistillate 

 flowers (n). 



Reproduction by stems in water plants. — General features. — 

 Aquatics rooted in the soil reproduce by underground stems and runners, 

 exactly as do land plants, except that migration usually is more rapid, 

 perhaps because of the easy penetration of the oozy slime at the bottom 

 of ponds. Some rhizomatous plants (as Hippuris, Limnanthemwm, and 

 species of Potamogeton) may advance as much as a meter a year, soon 

 filling a small pond (fig. 1165). The water lilies have gigantic rhizomes 



