IN THE VEGETABLE KINGDOM 47 



are propagated by seed, and those which are propagated 

 asexually by means of cuttings, buds, tubers, etc. When 

 a nurseryman raises a crop of cabbages for seed it is 

 obviously to his advantage that they should give as 

 large a yield of seed as possible. In such cases, unlike 

 apples, pears or oranges, the heavy yield of seed in no 

 way interferes with the edible qualities of the vegetable, 

 and if he can obtain as much seed as he requires from 

 a hundred cabbages instead of having to raise a thousand 

 it will make a considerable difference to his profits. As 

 a consequence, all plants which are propagated by seed 

 will be cultivated for a heavy yield of seed. On the other 

 hand, those plants in which a heavy yield of seed interferes 

 with their edible qualities are usually propagated asexually, 

 and the general rule is that asexually propagated plants 

 are selected for seedlessness. 



In examining the facts, then, we may expect from 

 our principle certain broad results. As wild plants are 

 usually developed under conditions of severe competition, 

 they will be adapted to produce their maximum degree 

 of fertility under relatively unfavourable conditions. 

 Consequently we may expect, as a general rule, that 

 their fertility will decline when they are transplanted to 

 the highly favourable conditions of cultivated gardens. 



We may expect tha.t plants which are cultivated for 

 a heavy yield of seed, or are propagated by seed, will 

 increase in fertility with increased favourability of con- 

 ditions up to a certain point (the optimum point for 

 fertility) ; but that when a certain point of favourability 

 has been passed fertility will begin to decline. 



We may expect that asexually propagated plants will 

 show a steady decline of fertility (i.e. production of fertile 

 seed) in proportion as they are highly cultivated. 



These anticipations are borne out by the facts with 



