APPENDIX 481 



After three years the length of the achene was reduced to less than 

 half, the breadth remaining almost unchanged. The effect of dry 

 conditions on the foliage was displayed, as shown in the following 

 note, in the marked tendency of the leaves of Bidens cernua to assume 

 the form of those of B. tripartita, those of the last-named species 

 remaining for the most part unchanged. Whilst plants of B. cernua 

 raised under the normal moist conditions as a rule developed only 

 lanceolate leaves, those grown from seed under unusually dry conditions 

 generally produced, in the case of the second, third, fourth, and fifth 

 pairs, the broad, deeply cut leaves of B. tripartita. The result of these 

 experiments are tabulated below. 



Effects of very dry Soil-conditions on the Growth of Bidens 

 CERNUA and Bidens tripartita. (Results stated in inches.)* 



* For the conditions of the experiments see above. 

 t For details consult the succeeding note. 

 + The plants died after flowering. 



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