432 



STUDIES IN SEEDS AND FRUITS 



The con- 

 nection 

 between the 

 late flo'vrer- 

 ing and the 

 Tiviparous 

 tendency of 

 the Ivy. 



The 



tendency to 

 vivipary 

 displayed by 

 acorns. 



There are therefore two singular features that must be 

 closely linked together in the life-history of the Ivy — the 

 autumnal flowering and the ripening of the seeds on the 

 plant during the winter, followed by germination in the spring, 

 without the intervention of a rest-period of more than a few 

 weeks' duration. Much depends on the causal connection 

 between them. If the plant is viviparous because it flowers 

 in the autumn, then the vivipary appears to be adaptive ; but 

 if it flowers late because it Is viviparous, then the autumnal 

 flowering would be an adaptation. It may be that the cause 

 of the late flowering is to be found in the absence of any 

 proper rest-period for the seed. For if the plant flowered in 

 the spring, it would mature its fruit at the close of the summer, 

 and the seedlings would be cut ofF by the winter's cold. The 

 retention of the viviparous habit would lead to extinction, 

 unless flowering occurred in the autumn. It is likely that a 

 diff^erence in the mode of ripening of the seeds may explain 

 why Hedera Helix (as stated by Kerner) grows in Central 

 Europe without any protection from the winter's cold, whilst 

 the Ivy of Southern Europe {Hedera poetarum), which is very 

 similar in characters, can only survive the winters of Central 

 Europe under a protecting roof. 



I come now to my observations on the normal tendency 

 to vivipary displayed by the seeds of acorns {Quercus Robur). 

 This is not only exhibited in the occasional germination of 

 these fruits on the tree, but in the actual stages of growth of 

 the seed within its shell before maturity is reached. The steady 

 growth of the seed on the tree long after the pericarp or shell 

 has begun to dry has been discussed at length in Chapter XIV. 

 It was then said that the tendency of a seed to continue its growth 

 on the plant after the pericarp or fruit-case has commenced to 

 dry and lose weight, finds its final expression in the germination 

 of the seed on the plant, or, in other words, in vivipary. Such 

 was the tendency displayed by the oaks near Salcombe, in South 

 D^von, during the successive autumns of 1908 to 191 1 ; and 

 doubtless it is characteristic of this tree in other localities. 



