374 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi. 



as, e.g., in the sporangia of vascular Cryptogams (whether 

 heterospory occur or not) and in the microsporangia or 

 anther-sacs of Gymnospenns and Angiosperms. As, further, 

 no doubt exists about the sporocyte nature of the embryo- 

 sac-cell we are compelled to explain the embryo-sac-cell on 

 the four-spore-hypothesis. 



Attention has already been drawn to the facts (p. 372) 

 that of the four nuclei (tigs. 20 and 23) of the embryo-sac, each 

 gives rise to two nuclei, each of which in their turn develops 

 into two cells (figs. 24, 25) ; that two groups of two cells 

 arise thus in the micropylar end of the sac {i.e., the two 

 synergidie -+- the ovum and the primordial cell), and that 

 finally each one of these four cells may play the part of a 

 sexual cell. lu other words, the two spores lying in the 

 micropylar half of the embryo-sac give rise to four sexual 

 cells, i.e., each spore gives rise to two sexual cells. 



A comparison with the male spores or pollen-grains renders 

 this explanation highly j^robable, for each pollen-grain 

 divides normally into a vegetative and a reproductive cell, 

 and the latter redivides, thus giving us two sexual cells for 

 each pollen-grain or spore. Four pollen-grains being formed 

 in each male sporocyte, and two reproductive cells in each 

 pollen-grain will make a total of eight reproductive cells 

 developed from one pollen-mother-cell, or male sporocyte. 



Similarly the female sporocyte or embryo-sac-cell gives 

 rise to four macrospores, and these in their turn to eight female 

 sexual cells. Tlie non-formation of cell-walls round the 

 four macrospores, as well as the absence of all vegetative 

 cells, may then be explained as due to the parasitic habit of 

 the spores. It is quite conceivable that the microspores, which 

 have to lead an independent existence for a longer or a 

 shorter time, should not have been reduced to the same 

 extent as the parasitic macrospores, and that for this 

 reason vegetative cells still occur in the former. 



Of tlie eight female sexual cells, one, the ovum or egg- 

 cell, is fertilised by a male sexual cell, namely, one of the 

 two sperm-cells developed from one pollen-grain ; two 

 sexual cells arising from dilTerent spores (the micropylar and 

 antipodal primordial cells) conjugate and give rise to one 

 large centrally placed cell, the primary endosperm-cell, the 

 nucleus of which corresponds to Strasburger's " secondary 



