ON BIASTREPSIS FN ITS RELATION TO CULTIVATION. 163 



The weakly plants were small and therefore required less space. 

 When the plants shot up in the following year, the one bed gave 8 

 per cent., the other only 3 per cent, of twisted stems. 



C. Influence of the soil. 



The richer the soil and the more vigorous the plants, the better 

 is the prospect for a high proportion of twisted stems. 



In the year 1891, in addition to the culture on good loose soil 

 (see p. 158), 1 had a control -experiment on poor hard ground. The 

 good soil was manured with 2 kilog. of guano and dried cow-dung 

 per square metre; the poor soil received only one-eighth of a kilog. 

 of guano per square metre; the treatment in other respects was 

 identical. The result was — 



On the good manured soil 34 % twisted stems 



On the poor soil 14 % „ „ 



In very poor soil the proportion of twisted stems may sink to 

 nothing. I made an experiment of this kind in 1894 with a bed 

 which consisted, to a depth of half a metre, of nothing but sand. 

 For seed I used two samples, gathered in 1891 and 1893, which 

 gave, in control-experiments, 10 per cent, and 25-30 per cent, of 

 individuals with spiral phyllotaxis; half a bed (4 square metres) was 

 sown with each of the samples. The seeds were covered with garden- 

 soil in order to ensure germination. The two half-beds gave respec- 

 tively 94 and 124 plants, that is 24 and 31 per square metre, which, 

 as they were for the most part small, only touched each other here 

 and there. The plants were examined in May 1895 and it was 

 found that, without exception, the phyllotaxis was decussate. 



This is a convenient opportunity to direct attention to a circum- 

 stance which has hitherto been insufficiently recognized in com- 

 parative experiments with plants: I refer to the inequality of exter- 

 nal conditions as regards the individual seedlings growing on one 

 and the same bed. This inequality is much greater than might be 

 supposed, especially during germination, it is a familiar fact that 

 the seeds of a sowing do not all germinate simultaneously; and 

 those which germinate on a sunny day in moist soil are at a great 

 advantage as compared with those which germinate in dry soil or 

 on a dull day. The unevenness of the surface of the soil leads to 

 some spots being dry and others relatively moist, and germination 

 is so much expedited in the latter that the seedlings are often found 

 growing in scattered groups. The mixture of the soil with the manure 

 is not uniform, even when the greatest care is taken; and this leads 



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