BOOTS 



33 



Pineapple family. Aerial orchids frequently possess roots of 

 peculiar structure, covered with a papery, absorbent layer 

 which takes up water freely when exposed to rain or dew. 

 One air plant, the Spanish moss (Tillandsia) (Figs. 367, 368), 

 common in the Gulf States, has no roots, 

 but it imbibes water freely by means of 

 special absorbing hairs scattered over the 

 surface of the plant. The Tillandsia is a 

 characteristic feature of many Southern 

 regions, often appearing as tangled, rope- 

 like masses hanging from the trees. 



33. Reproduction by means of roots. 

 Roots are often capable of producing buds 

 which may develop into new individuals 

 and thus serve to propagate the plant. 

 The sweet potato is a good instance of 

 this, each root if buried in moist sand 

 being capable of giving rise to several 

 new plants (Fig. 22). Roses are propa- 

 gated by root cuttings, and some trees, 

 such as the silver-leaved poplar (Populus) 

 and the black locust {Robinia), are very 

 troublesome because of the readiness with 

 which young sprouts (sometimes called 

 suckers) spring up from the roots. Many 

 bad weeds, such as the field sorrel (Rumex) 

 and the Canada thistle (Cirsium), are 

 reproduced by roots. In case of desirable 

 plants that can be propagated either by 



pieces of root or by seeds, it is generally better to use root 

 cuttings, as they will grow much faster. 



34. Duration of life and storage of food and water in roots. 

 It is usual to divide plants according to their duration of life 

 into three classes : annuals, living one year or less ; biennials, 

 living two years; perennials, living more than two years. 

 The boundaries between these classes are not always definite ; 



FIG. 22. Vegetative 



reproduction of the 



sweet potato 



The potato was buried in 

 moist sand and began to 

 sprout, that is, to send 

 out shoots from adven- 

 titious buds at various 

 points. Each shoot may 

 grow into a new plant. 

 About half natural size 



