Mr. C. Darwin on the Fertilization of Orchids. 151 



insects, and are gnawed by them, as in the case of many 

 Vandese and other exotic orchids. 



Goodyera repens (p. 114). — Mr. R. B. Thomson informs me 

 that in the north of Scotland he saAV many humble-bees visit- 

 ing the flowers and removing the pollen-masses, wdiich were 

 attached to their proboscides. The bee sent was Bombus ])ra- 

 torum. This species grows also in the United States ; and 

 Prof. Gray (Amer. Journ. of Science, vol. xxxiv. 1862, p. 427) 

 confirms my account of its structure and manner of fertiliza- 

 tion, which is likewise applicable to another and very dis- 

 tinct species, namely, Goodyera puhescens. Prof. Gray states 

 that the passage into the flower, which is at first very narrow, 

 becomes, as I suspected, more open during its older state. 

 Prof. Gray believes, however, that it is the column, and not 

 the labellum, which changes its position. 



Spiranthes autumyialis (p. 123). — As in the case of the 

 Goodyera^ Prof. Gray feels confident that it is the column which 

 moves from the labellum as the flower grows older, and not, 

 as I had supposed, the labellum which moves from the column. 

 He adds that this change of position, which plays so important 

 a part in the fertilization of the flower, "is so striking that 

 we Avonder how we overlooked it" (Amer. Journ. of Science, 

 vol. xxxiv. p. 427). 



On the rostellum o/Listera ovata not exploding spontaneously 

 (p. 149). — I have covered up some additional plants, and found 

 that the rostellum lost its power of explosion in about four days, 

 the viscid matter then turning brown within the loculi of the 

 rostellum. The weather at the time was unusually hot, and 

 this may have hastened the process. After the four days had 

 elapsed, the pollen had become very incoherent and some had 

 fallen on the two corners, or even over the whole sm-face, of 

 the stigma, which was penetrated by the pollen-tubes. Hence, 

 if insects should fail to remove the pollinia by causing the 

 explosion of the rostellum, this orchid certainly seems capable 

 of occasional self-fertilization. But the scattering of the in- 

 coherent pollen was largely aided by, and perhaps wholly de- 

 pended on, the presence of Thrips — insects so minute that 

 they could not be excluded by any net. 



Listera cordata (p. 152). — Prof. Dickie has been so good as 

 to observe the flowers on living plants. He informs me that, 

 when the pollen is mature, the crest of the rostellum is di- 

 rected towards the labellum, and that, as soon as touched, the 

 viscid matter explodes, the pollinia becoming attached to the 

 touching object ; after the explosion, the rostellum bends 

 downwards and spreads out, thus protecting the virgin stig- 

 matic surface ; subsequently the rostellum rises and exposes 



