132 HISTORY OF BOTANY 



I have just quoted was On the Various Contrivances by 

 which Orchids are Fertilised by Insects, which was really 

 an appendix to Sprengel's work, The Secret of Nature 

 Revealed, published in 1793, about which I spoke to you 

 recently, and aimed at supplying the missing key to 

 Sprengel's observation, viz. " that crossing played an 

 important part in keeping specific forms constant." 

 Darwin came to the further conclusion that " cross 

 fertihsation [or cross pollination, as we would call it 

 nowadays] is favourable to the fertihty of the parent 

 and to the vigour of the offspring," and that " all those 

 mechanisms which hinder self-fertiUsation and favour 

 crossing must be advantageous in the struggle for 

 existence ; and that the more perfect the action of the 

 mechanism the greater the advantage." 



This preHminary effort, which was pubUshed in 1862, 

 led Darwin to undertake a more extended enquiry into 

 the subject, under the title, The Effects of Cross- and 

 Self -Fertilisation in the Vegetable Kingdom, which did not 

 appear, however, until 1876. In the following year 

 another of his books was published dealing with The 

 Different Forms of Flowers on Plants of the Same Species, 

 in which he discussed the significance of the di- and 

 trimorphic flowers of Primula, Lythrum, Linum, Oxahs, 

 Viola, and other genera which showed this peculiarity. 



" In the course of the twenty years during which 

 Darwin was thus occupied in opening up new regions of 

 investigation to the botanist and showing the profound 

 physiological significance of the apparently meaningless 

 diversities of floral structure, his attention was keenly 

 alive to any other interesting phenomena of plant fife 

 which came in his way. In his correspondence he not 

 infrequently laughs at himself for his ignorance of sys- 

 tematic botany ; and his acquaintance with vegetable 

 anatomy and physiology was of the slenderest. Never- 

 theless, if any of the less common features of plant Hfe 

 came under his notice, that imperious necessity of seeking 



