158 Mr. C. Darwin on the Fertilization of OrcJdds. 



(p. 338). — In Orchis hircina, I clearly saw, under the micro- 

 scope, the whole front of the viscid disk become depressed as the 

 two pollinia together underwent the movement of depression. 



Number of seeds (p. 344). — The number of seeds produced 

 by Orchis macidafa, as given in my work, is small in com- 

 parison with that produced by some foreign species. I have 

 shown (Variation of Animals and Plants under Domestication, 

 vol. ii. 18G8, p. 379), on the authority of Mr. Scott, that a 

 single capsule o^ Acrojjera contained 371,250 seeds ; and the 

 species produces so many flowers and racemes, that a single 

 plant ])robably sometimes produces as many as 74 millions of 

 seeds in tlie course of a single year. Fritz Miiller carefully 

 estimated, by weighing, the number of seeds in a single capsule 

 of a Maxillaria in South Brazil, and found the number 

 1,756,440. The same plant sometimes produces half-a-dozen 

 capsules. 



Number of pollen-grains (p. 355). — I have endeavoured to 

 estimate the number of pollen-grains produced by a single 

 flower of Orchis mascula. There are two pollen-masses ; in 

 one of these I counted 153 packets of pollen ; each packet 

 contains, as far as I could count, by carefully breaking it up 

 under the microscope, nearly 100 compound grains ; and each 

 compound grain is formed of four grains. By multiplying 

 these ligures together, the product for a single flower is about 

 120,000 pollen-grains. Now we have seen that in the allied 

 0. maculata a single capsule produced about 6,200 seeds ; so 

 that there are nearly twenty pollen-grains for each ovule or 

 seed. As a single flower of a Maxillaria produced 1,756,000 

 seeds, it would produce, according to the above ratio, nearly 

 34 million pollen-grains, each of which, no doubt, includes 

 the elements for the reproduction of every single character in 

 the mature plant ! 



Enumeration of the Orch^dcas xohich^ as at present hnoivn, 

 habitually fertilize themselves (p. 358). — We have now seen 

 that self-fertilization habitually occurs, in a more or less perfect 

 manner, in one of the species of 0j>hrys, of Neotinea, Gymna- 

 denia^ Plafanthera, Epipactis^ Gephalantkera^ Neottia, and in 

 those Epidendreoi and in Dendrobium which often ])roduce 

 flowers tliat never expand. No doubt other cases will here- 

 after be discovered. Self-fertilization seems to be more per- 

 fectly secured in Ophrys apifera and in Neotinea intacta than 

 in tlie other species. But it deserves especial notice that in 

 all these orchids structures are still present, not in a rudimen- 

 tary condition, which are manifestly adapted for the trans))ort 

 by insects of tlic pollcn-masscs from one flower to anotlier. 

 As I have elsewhere remarked, some plants, both indigenous 



