156 VANDEiE. Chai'. VL 



the stigma to be seated at the bottom .jf a deep cavity, 

 low down in the column, or the anther to be seated 

 higher up, or the pedicel of the rostellum to slope 

 more upwards, &c. — all of which contingencies occur 

 in various species, — in such cases, an insect with a 

 pollinium attached to its head, if it flew to another 

 flower, would not place the pollen-masses on the 

 stigma, unless their position had become greatly 

 changed after attachment. 



This change is effected in many Vandese in the same 

 manner as is so general with the Ophrese, namely, by a 

 movement of depression in the pollinium in the course 

 of about half a minute after its removal from the 

 rostellum. I have seen this movement conspicuously 

 displayed, generally causing the pollinium to rotate 

 through about a quarter of a circle, i q several species 

 of Oncidium, Odontoglossum, Brassia, Vanda, Aerides, 

 Sarcanthus, Saccolabium, Acropera, and Maxillaria. 

 In Biodriguezia suaveolens the movement of depression 

 is remarkable from its extreme slowness ; in Eulophia 

 viridis from its small extent. Mr. Charles Wright, in 

 a letter to Professor Asa Gray, says that he observed 

 in Cuba a pollinium of an Oncidium attached to a 

 humble-bee, and he concluded at first that I was 

 completely mistaken about the movement of depres- 

 sion ; but after several hours it moved into the proper 

 position for fertilising the flower. In some of the 

 cases above specified in which the poliinia apparently 

 undergo no movement of depression, I am not sure that 

 there was not a very slight one after a time. In the 

 various Ophrese the anther-cells are sometimes seated 

 exteriorly and sometimes interiorly with respect to 

 the stigma ; and there are corresponding outward and 

 inward movements in the poliinia : but in the Vandeae 

 the anther-cells always lie, as far as I have seen, 



