IMPROVEMENT OF RACES. 351 



of other roots. Hence, if seeds are required of such plants, 

 they will be much more perfect if the tubers are removed. 



2. Deficiency of pullen. Some plants become so debili- 

 tated by cultivation, that the pollen of the stamen will not fer- 

 tilize the stigma of the pistil. In this case, the only remedy 

 is to bring pollen from some more vigorous plant, and apply 

 it, by artificial means ; a process only applicable to garden 

 plants. 



3. A moist, cold atmosphere, will prevent the pollen from 

 being formed ; and, if formed, from being thrown upon the 

 stigma. The fertilizing influence takes place only when the 

 plant is exposed to the warm dry air. Sometimes the pres- 

 ence of insects is necessary to convey the pollen to the stig- 

 ma ; and if they are absent, sterility will follow. 



4. The most frequent cause of sterility is the monstrous 

 condition of the floioers of many cultivated plants. The flow- 

 ers are nothing but modifications of the leaves ; the stamens 

 become florets in the course of cultivation, as always happens 

 in double flowers. Now it is evident, that when the stamens 

 are thus all changed, they cannot secrete pollen, and of course 

 there is nothing to fertilize the stigma. The stigma itself, 

 also, becomes changed. This can be remedied only by 

 planting, near by, the same species of plant which have either 

 stamens or pistils, as the case may be, and the requisite 

 quantity of pollen may be thus furnished. 



5. Many cultivated plants are grown in a climate different 

 from that in which they grow naturally. The process of 

 watering, also, often exposes the flowers and fruit organs to 

 decay. 



Such are some of the causes of the sterility of plants; and 

 it is evident, that if these and other causes do not operate 

 wholly to prevent seeds from ripening, they may weaken their 

 power of reproduction. As weak seeds will produce weak 

 plants, resource should be had to every means possible, to 

 give the highest degree of life and vigor to these indispensa- 



