1878.] 



President's A ddress. 



59 



The subject of the cross -fertilization of plants, which though a long 

 known phenomenon, first become a fruitful scientific study in Mr. 

 Darwin's now classical work " On the various contrivances by which 

 Orchids are fertilized," has within the last few years made rapid ad- 

 vance under its author's hand. The extreme importance of avoiding 

 self-fertilization might indeed be inferred from the prevalence in 

 flowers of elaborate contrivances for preventing it ; but it remained to 

 be shown that direct benefit attended cross-fertilization, and this has 

 now been proved by an elaborate series of experiments, the results of 

 which are not only that both increased fertility or greater vigour of 

 constitution attend cross-fertilization, but that the opposite effects 

 attend self-fertilization. In the course of these experiments it became 

 evident that the good effects of the cross do not depend on the mere 

 fact of the parents being different individuals, for when these were 

 grown together and under the same conditions, no advantage was 

 gained by the progeny ; but when grown under different conditions a 

 manifest advantage was gained. As instances, if plants of Ipomcea 

 and Mimulus, which had been self-fertilized for seven previous gene- 

 rations, were kept together and then intercrossed, their offspring did 

 not profit in the least ; whereas, when the parent plants were grown 

 under different conditions, a remarkably vigorous offspring was 

 obtained. 



Mr. Darwin's last work, " On the different forms of Flowers," 

 though professedly a reprint of his paper on dimorphic plants, pub- 

 lished by the Linnsean Society, contains many additions and new 

 matter of great importance concerning the behaviour of polygamous 

 plants, and on Cleistogamic flowers. Among other points of great 

 interest is the establishment of very close analogies between the pheno- 

 mena attending the illegitimate union of trimorphic plants, and the 

 results of crosses between distinct species, the sterile offspring of the 

 crosses of the same species exhibiting the closest resemblance to the 

 sterile hybrids obtained by crossing distinct species; while a whole 

 series of generalizations, founded on the results of the one series of 

 experiments, are closely paralleled by those founded on the other. 

 The bearing of this analogy on the origin of species is obviously 

 important. 



Besides these investigations, Mr. Darwin has produced within the last 

 five years second editions of his volume on the Fertilization of Orchids, 

 and on the Habits and Movements of Climbing Plants ; as also of his 

 early works on Coral Reefs, and Geological Observations in South 

 America ; all of them abounding in new matter. 



Of special interest to myself, as having been conducted in the 

 Jodrell Laboratory at Kew, are Dr. Burdon Sanderson's investi- 

 gations on the exceptional property possessed by the leaves and 

 other organs of some plants which exhibit definite movements in 



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