452 Tricotylous Races. 



(p. 332). It is natural to inquire, therefore, whether this 

 vigor of the seeds can be increased by improved nutri- 

 tion of the plant. Unfortunately we must, in such cases, 

 be content with averages, and these obviously give much 

 smaller differences than the single extreme cases. Some- 

 times I found that the external conditions exerted a con- 

 siderable influence, but, as a rule, I could not detect any 

 difference. 



In the first place I shall refer to the effects of manu- 

 ring. The prevailing opinion is that manuring with ni- 

 trates favors the development of leaves, but that phos- 

 phates favor flowers and fruits. As a nitrate manure 

 I employed horn-meal combined with dried guano and 

 as phosphate manure the ordinary superphosphate; but 

 I find that the former usually produces more abundant 

 flowering and a larger harvest of seed than the latter. 

 In 1899 I instituted a comparative experiment with Oeno- 

 thera Jiirfella by planting out the seedlings of a single 

 self-fertilized plant. During the period of flowering each 

 inflorescence was guarded from the visits of insects by 

 a parchment bag. The nitrate plants grew more ra])idly 

 and luxuriantly at first than those on the phosphate bed. 

 Moreover they began to flower somewhat earlier, and 

 consequently set more seed; for fertilization must be 

 stopped before all the flowerbuds have opened, since in 

 our climate flowers which open in September have not 

 time enough left to ripen their seed. 



The harvest for each individual plant was examined 

 separately, and from this was calculated, in the way we 

 have so frequently described, the percentage value for 

 each plant. In the following summary these are associ- 

 ated in groups of from 15-25, 26-35, 36-45; the means 

 of the groups being 20, 30, 40 etc. 



