214 



HUTCHINSON'S POPULAR BOTANY 



where they have withdrawn all their living material, they are preserved 

 from drying up, and when the rainy season begins they at once become 

 active above-ground, and the desert becomes a garden of brilliant flowers. 

 Such a transformation may be witnessed in the Karoo, in South Africa. 

 Among its plants the Brunsvigia is conspicuous by reason of its umbels of 

 scarlet flowers, which, it is said, may be seen at the 

 distance of a mile. 



Among certain plants with underground stems a 

 kind of motion occurs, to which it may be worth while 

 to make a brief allusion. Some plants, for example, 

 appear one season in a spot at a little distance from 

 that which they occupied in the previous season, and 

 thus appear to travel, the shifting of position being 

 effected by means of the sucker-like subterranean 

 stems annually formed by the parent, which projects 

 them to a certain distance and then perishes. The 

 corms of many plants of the Iris order (Iridacece) ex- 

 hibit a similar property, each forming a new corm at 

 its apex every year, which feeds upon the parent 

 till the latter is quite dry. Growth goes on in this 

 way, year by year ; the corms continually rising, not, 

 indeed, " by stepping-stones of their dead selves," but 

 by stepping-stones of their dead parents, " to higher 

 things," till the surface of the earth is reached. Then 

 the corms become dispersed by the scratching of birds 

 and small mammals, and each in its new position sends 

 a thick shoot deep into the soil, through which the 

 material of the above-ground corm is conveyed to 

 form a new one at a suitable depth, or, by the produc- 

 tion of special roots, the corm is pulled down to the 

 proper level. 



Yet the above instances of vegetable progression 

 have, after all, nothing very remarkable about them, 

 N^ the so-called motion being strictly analogous to the 



progression of an ordinary aerial stem by the forma- 

 tion of fresh branches year after year. True motion 

 does, however, exist in a large number of above- 

 ground stems, such as the tips of the runners or 

 stolons of the Strawberry-plant (Fragaria, fig. 278) and 



the growing points of the stems of the Ivy (Hedera), Raspberry (Rubus 

 idceus), etc., which Darwin, Sachs, and others have observed to rotate just 

 as do the cotyledons and rootlets of the Bean (Vicia faba\ Pea (Pisum 

 sativum\ Wood-sorrel (Oxalis acetosella), etc. Circumnutation is, indeed, 

 a general characteristic of aerial stems. 



Fia. 268. CHINESE 

 YAM (Dioscorea batatas). 



The tubers are a valuable 

 food, used like the Potato. 



