158 STRASBURGER : FERTILISATION OF PHANEROGAMS. 



cells thus successively produced, unite to form a connected cell- 

 complex, which lies within the grain, and is strongly arched forwards 

 into the comparatively large cavity of the generative cell. In the 

 case of the Coniferae, a similar vegetative cell-complex is formed in 

 the pollen grain, and this agrees so closely with that present in the 

 Cycadece referred to, that, as the author already mentioned has 

 maintained, it can scarcely be supposed to have another mode of 

 origin. Confirmatory evidence of the truth of this view is afforded by 

 the manner in which the vegetative cell-complex is developed in the 

 pollen grains of the Larch [Larix europcea). This has been care- 

 fully investigated by Strasburger himself, who finds that three 

 vegetative cells are successively cut off from the originally one-celled 

 pollen grain, though the two oldest of these become disorganised 

 soon after their formation. In other Coniferse, as in the genus 

 Finns, the differentiation is completed when the progamous cell has 

 divided once into a small vegetative cell and a larger generative cell. 

 With regard to the remaining group of Gymnosperms, the Gnetacece, 

 further knowledge is desirable, but Juranjd has established the fact 

 that in Ephedra altissima^ a cell-complex is present in the pollen 

 grain, and that it is produced in the same manner as in the other 

 groups. 



Hence it may be stated as a general rule, that the pollen grains 

 of Gymnosperms are not simple unicellular bodies, but contain one 

 comparatively large generative cell, and one or more smaller vegetative 

 cells. To this it may be added that in Cycads and Conifers, the genera- 

 tive cell gives origin to the pollen-tube, while the vegetative cells become 

 gradually shrivelled up. The same may probably be said of the 

 Gnetacece^ though definite information is wanting on this point. In 

 the Cycadece and CoJiiferce. the nucleus of the generative cell wanders 

 into the pollen-tube, and comes to rest near the growing end. This 

 nucleus divides once or oftener, and each of the daughter nuclei may 

 or may not become enveloped by a mass of protoplasm, which is 

 limited towards the outside by an ectoplasmic layer. 



By some authorities the cell-complex just described is regarded as 

 a rudimentary prothallium comparable to that of Ferns and the 

 Ligiilatce. Strasburger seems to question the validity of this view, 

 chiefly on the ground that its mode of development is quite different 

 from that of the so-called rudimentary prothallium of, Iso'etes and 

 Selaginella. 



Coming now to ordinary flowering plants, i.e., to Angiosperms, we 

 find the progamous pollen-cell dividing into a large and a small cell, 

 which have usually been regarded as the homologues of the genera- 

 tive and vegetative cells respectively of Gymnosperms. But here , 



Naturalist, 



