,336 CONCLUDING EBMAEKS Chap. VIH. 



enclosed within the anthers; but this is not so re- 

 markable a fact as was formerly thought, when the 

 case of Asclepias was alone known.* It is, however, 

 a wonderful sight to behold the tubes directing them- 

 selves in a straight line to the stigma, when this 

 is at some little distance from the anthers. As soon 

 as they reach the stigma or the open passage leading 

 into the ovarium, no doubt they penetrate it, guided 

 by the same means, whatever these may be, as in the 

 case of ordinary flowers. I thought that they might 

 be guided by the avoidance of light : some pollen-grains 

 of a willow were therefore immersed in an extremely 

 weak solution of honey, and the vessel was placed 

 so that the light entered only in one direction, lat- 

 erally or from below or from above, but the long 

 tubes were in each case protruded in every possible 

 direction. 



As cleistogamic flowers are completely closed they 

 are necessarily self-fertilised, not to mention the ab- 

 sence of any attraction to insects: and they thus 

 differ widely from the great majority .. of ordinary 

 flowers. Delpino believes f that cleistogamic flowers 

 have been developed in order to ensure the .production 

 of seeds under climatic or other conditions which tend 

 to prevent the fertilisation of the perfect flowers. I do 

 not doubt that this holds good to a certain limited ex- 

 tent, but the production of a large supply of seeds with 

 little consumption of nutrient matter or expenditure of 



* The case of Asclepias was de- emission of the tubes from the 



scribed by B. Brown. Baillon as- pollen-masses while still within 



serts-CAdansonia,' torn. ii. 1863, the anthers, in three. widely dis- 



p. 58) that with many plants the tinct Orchidean genera, namely 



tubes are emitted from pollen- Aceras, Malaxis, and' Xeottia : see 



grains which have not come into ' The Various ContnTances by 



contact with the stigma ; and that which Orchids are Fertilised,' 2nd 



they may be seen advancing hori- edit., p. 258^ 



zontally through the air towards t ' SuU' Opera la Distribuzione 



the stigma. I have observed the dei Sessi nelle Piante,' 1867, p. 30. 



