Mr. C. Darwin on the Fertilization of Orclilds. 7 



I may add tliat he cauglit the first-named motli, bearhig the 

 pollinia of this orchis, in my flower-garden, ahhough more 

 than a quarter of a mile distant from any spot where the plant 

 grows. I state in my work that I do not understand the cause 

 of the divergence of the pollinia so that they are enabled to 

 strike the lateral stigmatic surfaces ; but the explanation is 

 simjile. The upper margin of the nectary is arched, being 

 formed on one side by the disk of one pollinium, and on the 

 other side by the other disk. Now if a moth inserts its pro- 

 boscis obliquely, and there are no guiding-ridges by which, as 

 in Anacamptls pyramidalls, a moth is compelled to insert its 

 proboscis directly in front, or if a bristle be inserted obliquely, 

 one pollinium alone is removed. In this case the pollinium 

 becomes attached a little on one side of the bristle or proboscis ; 

 and its extremity, after the vertical movement of depression, 

 occupies a proper position ior striking the lateral stigma on 

 the same side. 



On the Gymnadenia tridentata of North America (p. 83). — 

 Prof. Asa G-ray has published (American Journal of Science, 

 vol. xxxiv. 1862, p. 426, and footnote p. 260 ; and vol. xxxvi. 

 1863, p. 293) some interesting notes on the Gymnadenia 

 tridentata. The anther opens in the bud, and some of the 

 pollen invariably falls on the naked cellular tip of the rostel- 

 lum ; and this part, strange to say, is penetrated by the pollen- 

 tubes, so that the flowers are self-fertilized. Nevertheless 

 "all the an-angements for the removal of the pollinia by insects 

 (including the movement of depressien) are as perfect as in the 

 species which depend upon insect aid." Hence there can be 

 little doubt that this species is occasionally crossed. 



Hahenarla or Platanthera hlfoUa (p. 88). — According to 

 Dr. H. Miiller, of Lippstadt, PI. blfolia of English authors is 

 the PL solstitlalis of Boenninghausen ; and he fully agrees 

 with me that it must be ranked as specifically distinct from 

 PI. cMorantha. Dr. llliller states that this latter species is 

 connected by a series oi gradations witli another form which 

 in Germany is called PI. blfolia. He gives a very full and 

 valuable account of the variability of these species of Platan- 

 thera and of their structure in relation to their manner of fer- 

 tilization. (See Yerhandl. d. Nat. Verein. Jahrg. xxv. III. 

 Folge, V. Bd. pp. 36-38.) 



American species of Platanthera (p. 91). — Prof. Asa Gray 

 has described (American Journal of Science, vol. xxxiv. 1862, 

 pp. 143, 259, & 424, and vol. xxxvi. 1863, p. 292) the stmc- 

 ture of ten American species of Platanthera. Most of these 

 resemble in their manner of fertilization the two British spe- 

 cies described by me ; but some of them, in which the viscid 



