ON BIASTREPSIS IN ITS RELATION TO CULTIVATION. 167 



Hence, when the shoots are thrown up, they are too weakly to 

 develop spiral phyllotaxis. This result accords fully with those 

 obtained in my observations on the effects of too limited space and 

 bad soil. 



E. Autumn-sowings in the open. 



1 began an experiment on September 11, 1891, which may be 

 regarded as a control to the summer-sowings. The seedlings which 

 are produced in a sowing so late in the season do not throw up their 

 shoots in the following year, but remain in the rosette-stage, the 

 plants growing vigorously until the following autumn. They do not 

 throw up their shoots until the third year. The lateness of the 

 sowing has, therefore, the effect, not of weakening, but of materially 

 invigorating the plants. 



At the beginning of the first winter the young plants had only 

 two or three pairs of leaves, which were not much more than 3 cm. 

 in length. It is known that the throwing up of the shoot of biennials 

 in general is the result of stimulation and that this stimulation is 

 given by the winter. Indeed, when Rape is sown early, this effect 

 may be produced by the late night-frosts. But if the plants are too 

 young they appear not to be susceptible to this stimulation. This is 

 a phenomenon which has been too much overlooked by physiologists. 



In the middle of September 1892 just one year after sowing, 

 I examined the plants. There were twenty-three of them in a small 

 bed of 2 square metres area. Not one of them had thrown up a 

 shoot; but ten of them (44 per cent.) showed spiral phyllotaxis in 

 the heart of the rosette and four had three-leaved whorls. 



Hence it appears that the effect of the prolongation of the rosette- 

 stage is rather to increase than to diminish the proportion of ab- 

 normal plants. Moreover, this experiment leaves no doubt as to 

 the correctness of the interpretation which I have placed upon the 

 results of summer-sowing. 



F. Autumn-sowings in the greenhouse. 



The object of these experiments was so to accelerate, by culti- 

 vation in a greenhouse under favourable conditions of temperature, 

 illumination, etc., the germination of the seeds and the subsequent 

 growth of the seedlings during the autumn and the winter, that the 

 plants should be in a position to throw up their shoots in the follo- 

 wing summer. In order to maintain the earth in the pots, day and 

 night, as nearly as possible at the temperature (22° C.) which I found 



