372 



STRASBURGER ON FOREIGN POLLINATION. 



follow ; in others, again, fertilisation was in process and presented 

 the usual phenomena ; while, lastly, in some ovules a rudimentary 

 embryo was already formed. These rudiments were partly normal 

 and partly abnormal in appearance, but ultimately all died. From 

 these facts it may be inferred that the fertilisation and the develop- 

 ment of the embryo are here effected under conditions of some 

 difficulty, and are therefore not carried to a successful termination. 

 Incidentally too, they point to a possible explanation of the well-known 

 circumstance that hybridisation often yields only a few seeds capable 

 of germinating, and frequently gives rise to mal-formed embryos. 



Similar experiments with other species of Orchis gave similar 

 results, but in the case of Orchis latifolia pollinated with O. mascula, 

 tolerably numerous embryos of normal appearance were developed, 

 some of which attained maturity and ripened themselves fully. On 

 these, however, there is no need to dwell, as hybrids are well known 

 to occur among orchids, not merely within the limits of the same 

 species, but between members of distinct genera. 



Besides experimenting as described, Strasburger also tried the 

 effect of placing pollen on the transverse section of the style after 

 the removal of the stigma, and also of placing pollen directly in the 

 cavity of the ovary. As might be expected, the results in both cases 

 were very various, both when proper and foreign pollen was employed. 

 When treated with their own pollen some plants produced as good 

 seed after pollination in these irregular ways as after pollination of 

 the stigma, and with foreign pollen the degree of pollen-tube 

 formation differed in different cases. Thus, however useful as a 

 receptive surface, and as a suitable nidus for the germination of the 

 pollen, the stigma is not an indispensable portion of the sexual 

 apparatus. 



The fact having been established that heterogeneous plants are 

 capable of forming pollen-tubes on one another, Strasburger next 

 enquired whether social plants are protected against this, especially 

 those that are wind-fertilised. He found that the pollen of Plantago 

 lanceolata germinates on the stigma of Ranunculus acris, and sends 

 its tubes into the style, so that in this Ranunculus there would seem 

 to be no protection against wind-fertilised neighbours. On the other 

 hand, the pollen of Plantago did not germinate on Stellaria Holostea. 

 In the converse experiments, pollen from Ranunculus acris was 

 found to put forth a few short tubes on the stigma of Plantago 

 lanceolata, while that from Stellaria Holostea developed vigorous 

 tubes which entered a good way into the style. 



In this connection the Graminece are obviously of special interest, 

 but there are many difficulties in the way of obtaining decisive results 



Naturalist, 



