Mr. C. Darwin on the Fertilization of Orchids. 153 



— I may here remark that Delpino (Fecondazione nelle Piante, 

 Firenze, 1867, p. 19) says he has examined flowers of Vanda, 

 Ej)idendron, FhaiuSj Oncidium, and Defidrobiunij and con- 

 firms my general statements. The late Prof. Bronn, in his 

 German translation of this work (1862, p. 221), gives a de- 

 scription of the structure and manner of fertilization of Stan- 

 hoj)ea devoniensis. 



Sexes of Acro'persi ?iot separated {p. 206). — I have committed 

 a great error about this genus, in supposing that the sexes 

 were separate. Mr. J. Scott, of the Royal Botanic Garden of 

 Edinburgh, soon convinced me that it was an hermaphrodite, 

 by sending me capsules containing good seed, which he had 

 obtained by fertilizing some flowers with pollen from the same 

 plant. He succeeded in doing this by cutting open the stig- 

 matic chamber, and inserting the pollen-masses. My error 

 arose from my ignorance of the remarkable fact that, as shown 

 by Dr. Hildebrand ( Botanische Zeitung, 1863, Oct. 30 et 

 se^'., and Aug. 4, 1865), in many orchids the ovules are not 

 developed until several weeks or even months after the pollen- 

 tubes have penetrated the stigma. No doubt if I had exa- 

 mined the ovaria of Acr opera some time after the flowers had 

 withered, I should have found well-developed ovules. In 

 many exotic orchids besides Acropera (namely, in Gongora^ 

 Cirrhcea, Acineta, Stanhopea, &c.), the entrance into the stig- 

 matic chamber is so narrow that the pollen-masses cannot be 

 inserted without the greatest difficulty. How fertilization is 

 effected in these cases is not yet knoAvn. That insects are the 

 agents there can be no doubt ; for Dr. Criiger saw a bee {Eu- 

 glossa) with a pollinium of a Stanhopea attached to its back j 

 and bees of the same genus continually visit Gongora. Fritz 

 Miiller has observed, in the case of Cirrhma (Bot. Zeitung, 

 Sept. 1868, p. 630), that if one end of the pollen-mass be in- 

 serted into the narrow entrance of the stigmatic chamber, this 

 part, from being bathed by the stigmatic fluid, swells, and the 

 whole pollen-mass is thus gradually drawn into the stigmatic 

 entrance. But, from observations which I have made on 

 Acropera and Stanhopea in my own hot-house, I suspect that, 

 with many of these orchids, the pedicel with the narrow end 

 of the pollinium, and not the broad end, is ordinarily inserted 

 into the stigmatic chamber. By thus placing the pollinium, 

 I have occasionally succeeded in fertilizing some of these 

 orchids, and have obtained seed-capsules. 



Structure and fertilization of the Vandeas &c. of Brazil 

 (p. 210). — Fritz Miiller has sent me many letters containing an 

 astonishing number of new and curious observations on the 

 structure and manner of cross-fertilization of various orchids 



