482 STUDIES IN SEEDS AND FRUITS 



NOTE 14. (See previous note.) 



Are Bidens cernua and Bidens tripartita distinct species ? 



It seems questionable whether the distinction between these two 

 allied species is always maintained, a distinction depending on diiFerences 

 in the leaves and possibly concerned mainly with their stations, Bidens 

 cernua preferring the wet borders of ponds and ditches and B. tripartita 

 the river-bank, the last growing more frequently out of the water than 

 does B. cernua. This preference for a drier station on the part of B. 

 tripartita acquires interest from the fact brought out in the experi- 

 .ments discussed in Note 13, and referred to below, that plants raised 

 from seeds of B. cernua in very dry conditions develop foliage like that 

 of B. tripartita. Many years since, I took a great interest in these 

 two plants ; and individuals presenting characters intermediate between 

 those of the two species came often under my notice. The two may be 

 sometimes observed growing side by side ; and occasionally in the midst 

 of a patch of one species will be seen a single individual of the other. 



It is of importance to record that when raised under unusually dry 

 conditions, as described in Note 13, the young plants differed but 

 slightly from each other, broad tripartite leaves being commonly pro- 

 duced by both species in the case of the second, third, fourth, and fifth 

 pairs. The specific difference began to be exhibited after the fifth 

 pair of leaves, the plants of B. cernua developing afterwards only 

 undivided lanceolate leaves, whilst those of B. tripartita continued to 

 produce their typical foliage until the eighth pair, when they put forth 

 two or three pairs of lanceolate leaves under the flower-head. 

 Occasionally plants of B. cernua raised under these very dry conditions 

 produced broad leaves of the type of those of B. tripartita., except that 

 they were undivided. 



Plants of B. cernua raised in my greenhouse under normal condi- 

 tions in muddy water and in wet soil developed only the characteristic 

 lanceolate leaves, and it was only when exposed to the dry conditions 

 of my experiments that they began to produce foliage like that of 

 B. tripartita. Grown under natural conditions the young plants of 

 both species generally put forth their typical leaves in the third pair. 



NOTE 15 (p. 325). 



The proportions of pericarp and seeds in the fruit of Theobroma 

 Cacao (Cocoa). 



The following data were kindly supplied to me in 1909 by Mr R. 

 D. Anstead, superintendent of the Botanic Gardens in Grenada. 



