296 Mr Carry, On the Development of [Nov. 27, 



Zostera L., while Asclepias Cornuti Dene, must now be added to 

 this interesting list of exceptions to what is the otherwise uni- 

 versal rule in Phanerogamous plants. 



I may here allude to the circumstance that after extremely 

 careful observations many times repeated I have at length in 

 several cases satisfactorily traced the passage for some distance of 

 the larger of the two nuclei in the pollen-grain into the long cel- 

 lulose tube which it puts forth when the pollinium ruptures in 

 consequence of its being placed in immediate contact with the 

 stigma, although I have been unable to follow its changes further. 

 The larger nucleus of the pollen-grain does not then in this genus 

 become broken up and diffused through the protoplasmic con- 

 tents of the grain immediately before the production of the pollen- 

 tube, as Strasburger has shewn that it does in many other flower- 

 ing plants, but simply passes in its entire concrete form into the 

 pollen-tube. What becomes of the smaller nucleus I cannot 

 definitely state, but I have reason to believe that it is left in the 

 grain, or perhaps dissolved, since I have never been able to trace 

 its passage into the pollen-tube, although I have carefully 

 watched for it. 



The ultimate changes and fate which the tapetal membrane 

 undergoes appear to be as follows : — 



The cells composing it which lie on the outer side of the 

 anther divide, each by means of a vertical tangential wall, 

 parallel to the original tangential walls of the cell, so that the 

 membrane becomes two cells broad on this side. Those tan- 

 gential cell-walls, which are farthest from the pollinium, in that 

 row of limiting cells which is next the cavity of the loculus, toge- 

 ther with the adjacent portions of the radial walls of these cells 

 become broken down and disintegrated. On the other hand the 

 tangential walls which are nearest the pollinium, together with the 

 internal 1 portions of the said radial walls, persist for some time form- 

 ing a continuous membrane surrounded by a layer of small cells. 

 These latter are on the outer side of the anther, segments from 

 those cells derived from the parenchyma that completed the tapetum 

 proper on this aspect, and on the inner side of the anther are the 

 row of cells formed immediately external to the tapetum proper at 

 the same time that it was differentiated and which have persisted. 

 Such is the condition immediately prior to the opening of the two 

 loculi to expose the pollinia, the method of which is intimately 

 connected with the presence of other contrivances in the flower 

 for ensuring pollination by the agency of insects. This change 

 occurs by almost the whole of the parenchymatous tissue forming 

 the substance of the anther, together with the remains of the 



1 With relation only to the loculus. 



