Alternating Annual and Biennial Habit. 303 



as annuals, and of late I have grown all my cultures by 

 this method or by some .slight modification of it. 



In order to determine the effect of the soil on the 

 development of the stem I have compared the difference 

 l)etween plants grown on manured and unmanured beds, 

 and also the difference between plants grown on barren 

 sand and on fertile soil. The first of these two exi)eri- 

 ments I have made with the Oenothera laevifolia. I 

 used seeds which I had saved in 1890 from the third 

 annual generation of my culture (see Vol. I, p. 273). 

 The seeds were sown in the middle of May on three 

 beds of 3/4 scjuare meters each. They were adjacent to 

 one another, had the same soil, a similar exposure, and 

 so forth. The seedlings were thinned out early, to 100 

 per bed, in such a way that the distances between them 

 were as uniform as possible. The sole difference lay 

 in the kind of manure which they received, which in 

 No. 1 was nothing, in No. 2 a quarter of a kilo of guano, 

 and in No. 3 a quarter of a kilo of hornmeal. In the 

 second bed, therefore, the manure was rich in phosphatef 

 and in the third in nitrogen. On the 30th of July 1 

 recorded the plants w'ith the following result : 



In spite, therefore, of the fact that the race had been 

 selected for three years the proportion of annual plants 

 on the bed without manure was only 77 per cent, wliilst 

 this proportion was considerably increased by the addi- 

 tion of manure, and more bv the addition of nitroq:en 

 than by that of phosphates. Further experiments with dif- 

 ferent quantities of the same manure showed that the 



