858 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi. 



impression, as Ward points out distinctly, of being similar in 

 nature to those preceding it. We know, further, that the walls 

 of spore-mother-cells " (i.e., sporocy tes) " break down when- 

 ever spores are reaching their maturity — that they are, in other 

 words, very transient ; in the em1)ryo-sac this process of dis- 

 solution of the wall seems to take place even before spore- 

 formation, or rather no definite wall can be laid down, partly 

 due to the vacuole," &c. 



I was led to criticise my own paper on reading an article 

 by Guignard,* on the formation of sexual nuclei in plants, 

 who comes to the conclusion that the nucleus of a pollen- 

 mother-cell (sporocyte) is comparable to the primary nucleus 

 of the embryo-sac, as he finds that in Lilmm Martagon both 

 nuclei contain at the time of their formation twenty-four 

 chromatin-segments, and that on their division each daughter- 

 nucleus contains only twelve segments, i.e., the number of 

 chromatin-segments has been reduced by half in the four 

 pollen-grains and in the eight nuclei within the embryo-sac, — 

 a deficiency to be made up again at the time of fertilisation. 

 A similar reduction in the number of chromatin-segments is 

 stated to occur in Fritillaria, Tidiya, Allium, Ahtrwmcria and 

 Listcra. The nuclei of the pollen-mother-cell (sporocyte) and 

 of the embryo-sac being thus comparable, the author comes 

 to the conclusion that the embryo-sac is comparable to the 

 pollen-mother-cell, i.e., it must be a sporocyte. 



How this discovery affects our interpretation of the eight 

 structures within the embryo-sac, I shall discuss after I have 

 described the changes in the embryo-sac leading to the forma- 

 tion of the two groups of four nuclei. 



Before proceeding with the investigation as to the fate of 

 the young embryo-sac and its sister-cells, I shall state briefly 

 the changes in the non-physiological archesporia, and describe 

 shortly the early development of the single integument of 

 the ovule. 



The non-physiological archesporia, some of which, in direct 

 contact with the true archesporium, equal the latter in size 

 during the early stages of development (fig. 1), soon undergo 

 oljlique divisions (figs. 2, o ; x has been placed on the 

 oljlique division-walls) and periclinal divisions (fig. 7 on the 



* Cornptos RcndiiH, oxii., 1891, p. 1074. My ;ittciitioii was drawn to this 

 pajx;!- by a review in the Trans. Roy. Micr. Soc, London. 



