I 



CilAP. IX. MOVEMENTS OF THE POLLINIA. 273 



E, p. 18) the two iiaps or sides contract and curl inwards ; 

 and this causes the divergence of the pollinia. By a 

 kind of contracti()n two valleys are likewise formed in 

 front of the caudicles, so that the latter are thrown 

 forwards and downwards, almost in the same way as if 

 trenches were dug in front of two upright poles, and 

 then carried on so as to undermine them. As far as I 

 could perceive, an analogous contraction causes the 

 depression of the pollinia in Orchis mascula. With 0. 

 liircina both pollinia are attached to a single rather large 

 square disc, the whole front of which, after exposure 

 to the air, sinks down and is then separated from the 

 liinder part by an abrupt step. By this contraction both 

 pollinia are carried forwards and downwards. 



Some pollinia which had been gummed on card for 

 several months, when placed in water, rose up and 

 afterwards underwent the movement of depression. 

 A fresh pollinium, on being alternately damped and 

 exposed to the air, rises and sinks several times alter- 

 nately. Before I had ascertained these facts, which 

 show that the movement is simj^ly hygrometric, I 

 thought that it was a vital action, and tried vapour 

 of chloroform and of prussic acid, and immersion in 

 laudanum : but these reagents did not check the 

 movement. Nevertheless, there are some difiiculties 

 in understanding how the movement can be simply 

 liygrometric. The flaj^s of the saddle in Orchis pijra- 

 midcdis (see fig. 3, D, p. 18) curl completely inwards 

 in nine seconds, which is a surprisingly short time 

 for mere evaporation to produce an effect ;* and the 



* Tliis fact does not now appear awn of Stipa twists and untwists 



to me so surprising as it formerly wlien exposed to dry and danjp air. 



did, for my sou Francis lias shown These movements" being due, as 



'• Transact. Linn. Soc' 2nd series. he has shown, to the twistin"- and 



Bit. vol. i. ISTO, p. 149) witli untwisting of the separate cells, 

 what extraordinary (luickne.si tLe 



