176 STRASBURGER : FERTILISATION OF PHANEROGAMS. 



pollen-tube reaches a papilla, dissolves its wall at the poiJit of contact^ 

 and enters into the cell-lumen. When the tip of the growing tube 

 reaches the base of the papilla, it bursts through the same into the 

 conducting tissue of the style, along which it advances between the 

 walls of the cells to the ovary. The Malvacea. behave like Githago up 

 to a certain point, and then present special peculiarities. Thus, when 

 the pollen-tube has burst through the base of the papilla, and entered 

 the conducting tissue, it does not immediately advance further. The 

 contents of the pollen-grain collect themselves into an elongated, 

 elliptical mass, with an irregular contour, and pass out of the grain. 

 Then the aggregated contents grow down the conducting tissue, with 

 a thick tube, the entire mass flowing onwards, and reminding the 

 observer of the movement of a Plasinodiuni. 



It will be understood that these are not the only methods by 

 which the entrance of the pollen-tubes is effected, but they are the 

 mxost important and the most typical. They will recall, at least to 

 the minds of fungologists, and that in a most striking manner, the 

 modes by which the hyphae of parasitic Fungi gain admission to the 

 tissues of the host-plant. 



Having thus described the structure of the pollen-grain, the 

 development of the pollen-tube, and the way in which the latter finds 

 an entrance into the ovary, Strasburger proceeds to the later stages 

 of the fertilisating process. In the Co?iiferce, which are dealt with in 

 the third section, the most important morphological facts are already 

 tolerably well known, and Strasburger has little to add thereto. It is 

 common knowledge indeed that here the process of fertiUsation is 

 actually a process of copulation between the nucleus of the oosphere or 

 egg-cell, as Strasburger often calls it, and the generative cell-nucleus^ 

 which enters the corpusculuni, or secondary embryo-sac, from the 

 pollen-tube Hence our author does not dwell upon the essentials of 

 the process, but examines two or three subordinate questions which 

 are still under discussion. As these are of secondary importance 

 only, we may pass them by, at least for the present, and follow him 

 into the fourth section, where the case of the Angiosperms is subjected 

 to careful and extended treatment. 



In many of these plants, as everyone who has attempted to in- 

 vestigate the matter knows well, there are great difficulties in the way 

 of decisively determining what actually occurs after the pollen-tube 

 has entered the micropyle of the ovule. Strasburger's attempts to 

 overcome these difficulties have, thus far, been partially successful 

 only ; and hence he has been in the main restricted to those plants, 

 which by virtue of the transparency of their ovules, a.lloAv the neces- 

 sary observations to be made. The orchids appear to have been 



Naturalist, 



