Stability and Real Atavism 159 



respect to their stability by different writers 

 and at different times. In doing this it is plain 

 that it is very essential to be sure of the purity 

 of the seed. Specimens must be grown in posi- 

 tions isolated from their allies, and if possible 

 be pollinated artificially with the exclusion of 

 the visits of insects. This may be done in differ- 

 ent ways. If it is a rare species, not cultivated 

 in the environment, it is often sufficient to make 

 sure of this fact. Pollen may be conveyed by 

 bees from distances of some ten or twenty 

 meters, or in rare cases from some hundred 

 meters and more, but a greater distance is or- 

 dinarily sufficient for isolation. If the flowers 

 fertilize themselves, as is more often the case 

 than is generally supposed, or if it is easy to 

 pollinate them artificially, with their own pollen 

 or in small groups of similar individuals, the 

 best way is to isolate them by means of close 

 coverings. When flowering, the plants are as a 

 rule too large to be put under bell-glasses, and 

 moreover such coverings would keep the air 

 moist, and cause the flower buds to be thrown 

 off. The best 'coverings are of netting, or of 

 canvas of sufficiently wide mesh, although after 

 a long experience I greatly prefer screens of 

 fine iron-wire, which are put around and over 

 the whole plant or group of plants, and fastened 

 securely in the ground. 



