172 VANDE^. Chap. VI, 



into it only with extreme difficulty. In the case of 

 Cirrhsea, he found that this could be effected more 

 easily, after they had shrunk a little from being left 

 to dry for half an hour or an hour. He observed two 

 flowers with pollen-masses naturally inserted by some 

 means into .their stigmas. On several occasions after 

 forcing the end of a pollen-mass into the mouth of the 

 stigma, he witnessed a most curious process of deglu- 

 tition. The extremity of the pollen-mass swells from 

 imbibing moisture, and as the chamber gradually 

 widens downwards, the swelling part is forced down- 

 wards ; so that the whole is at last drawn inwards and 

 disappears. In the case of Notylia, Tritz Miiller ob- 

 served that the entrance into the stigma became a 

 little larger after the flower had remained expanded 

 for about a week. In whatever manner this latter 

 plant is fertilised, it is certain that it must be im- 

 pregnated with pollen from a distinot plant ; as it 

 offers one of those extraordinary cases in which its own 

 pollen acts like poison on the stigma. 



In the last edition of this work it was shown that 

 the ovaria of mature flowers of Acropera do not con- 

 tain any ovules. But I erred greatly in the interpre- 

 tation of this fact, for I concluded that the sexes were 

 separate. I was however soon convinced of my error 

 by Mr. Scott, who succeeded in artificially fertilising 

 the flowers with their own pollen. A remarkable dis- 

 covery by Sildebrand, * namely, that in many Orchids 

 the ovules are not developed unless the stigma is 

 penetrated by the pollen-tubes, and that their develop- 

 ment occurs only after an interval of several weeks 

 or even months, explains the state of the ovarium 

 in Acropera, as observed by me. According also to 



■ Bot. Zeitung,' 1863, Oct. 30, et seq., and Aug. i, 1865. 



