STRASBURGER ON FOREIGN POLLINATION. 37 1 



and vigorous Friiillaria pollen-tubes were simultaneously produced ; 

 but when the latter were given 24 hours' start, they did not prevent 

 the former from developing normally, entering the ovary, and later 

 on completing the fertilising process. Hence pollinating with foreign 

 pollen, even when the latter is capable of forming pollen-tubes, need 

 not be disadvantageous to the plant concerned. 



On dicotyledonous plants the experiments with the pollen of 

 Fritillaria did not succeed in causing the development of vigorous 

 pollen-tubes, and on this account the experiments in this direction 

 were chiefly made with Agapafithus umbellatus. On the stigma of 

 Achimenes grandiflora the pollen of Agapanthus umbellatus germinates 

 readily, the tubes growing deep down into the style and building 

 numerous drops of cellulose. This shows that even monocotyle- 

 donous pollen is capable of vigorous development on a dicotyle- 

 donous stigma. On the contrary, however, the pollen of Achimenes 

 grandiflora did not germinate on Agapanthus, so that here is a case 

 of failing reciprocity. On Nicotiana tabacum only a portion of the 

 pollen grains of Agapanthus germinate, but these form tubes of very 

 considerable length, the poisonousness of Nicotiana offering appa- 

 rently no hindrance to their development. Moreover, Nicotiana 

 pollen produced very good tubes on Agapanthus which penetrated a 

 distance far into the style, and thus furnished an example of vigorous 

 development of dicotyledonous pollen on a monocotyledonous stigma. 

 A very beautiful illustration of this is also afforded by the behaviour of 

 Lathyrus montanus on Convallaria latifolia, where the pollen-tubes 

 of the Lathyrus actually reach the cavity of the ovary of the Conval- 

 laria. The pollen of Lathyrus montanus germinates well also on 

 Orchis Morio, though the tubes do not penetrate into the ovary and 

 have but an inconsiderable influence on the development of the ovules. 



In the cases hitherto referred to, which are typical of numerous 

 experiments recorded by the author, the pollen grains germinated on 

 the foreign stigma, but the fertilising process was not completed by 

 the entrance of the tube into the micropyle and the copulation of 

 the sperm nucleus with that of the egg-cell or oosphere. But in 

 others, a nearer approach to complete fertilisation was exhibited. 

 Thus, specimens of Orchis Morio were pollinated with Orchis fusca. 

 In a short time pollen-tubes were put forth in the normal way, and 

 grew down into the ovary, stimulating, as usual, the development of 

 the ovules. By the time the egg-apparatus was fully formed in the 

 embryo-sac, the ends of the pollen-tubes had turned to the ovules, 

 and soon entered the micropyle. In many ovules the embryo-sac 

 shrivelled before the entrance of the pollen-tube ; in others the tip 

 of the pollen-tube reached the embryo-sac, but fertilisation did not 



Dec. 1886. 



