28S CONCLUDING EEMARKS. Chap. IX. 



It may naturally be inquired, Why do the Orchideae 

 exhibit so many perfect contrivances for their fertili- 

 sation? From the observations of various botanists 

 and my own, I am sure that many other plants offer 

 analogous adaptations of high perfection ; but it seems 

 that they are really more numerous and perfect with 

 the Orchideae than with most other plants. To a 

 certain extent this inquiry can be answered. As each 

 ovule requires at least one, probably several, pollen- 

 grains,* and as the seeds produced by Orchids are so 

 inordinately numerous, we can see that it is necessarv 

 that large masses of pollen should be left on the stigma 

 of each flower. Even in the Keottese, which have 

 granular pollen, with the grains tied together by weak 

 threads, I have observed that considerable masses of 

 pollen are generally left on the stigmas. This cir- 

 cumstance apparently explains why the grains cohere 

 in packets or large waxy masses, as they do in so 

 many tribes, namely, to prevent waste in the act of 

 transportal. The flowers of most plants jDroduce pollen 

 enough to fertilise several flowers, so as to allow of or to 

 favour cross-fertilisation. But with the manv Orchids 

 which produce only two pollen-masses, and with some of 

 the Malaxea3 which produce only one, the pollen from 

 a single flower cannot possibly fertilise more than two 

 flowers or only a single one ; and cases of this kind 

 do not occur, as I believe, in any other group of 

 plants. If the Orchidete had elaborated as much 

 pollen as is produced by other plants, relatively to the 

 number of seeds which they yield, they would have 

 had to produce a most extravagant amount, and this 

 would have caused exhaustion. Such exhaustion is 

 avoided by pollen not being produced in any great 



• Giirtuer, 'Beitrage zur Kenntniss der Befruchtung,' 1S41, p. 135. 



