June 1891.] BOTANICAL SOCIETY OF EDINBURGH. 143 



in the embryo-sac, while the antipodal prothallus gives rise 

 to one primordial sexual cell ; that by the conjugation of two 

 primordial sexual cells a fertilised cell arises, namely, the 

 endosperm-cell, which has the power of further development 

 into a tissue, the endosperm, when by the fertilisation of the 

 remaining sexual cell of the micropylar prothallus, the egg- 

 cell, by an extraneous sexual-cell, the product of the pollen- 

 grain, an impetus has been given to the flow of nutritive 

 material into the ovule. Further, that the embryo resulting 

 from the fertilisation of the egg- cell by a pollen-grain 

 is more vigorous than the embryo resulting from the 

 conjugation of the two sexual cells arising in the em- 

 bryo-sac, and that in consequence we have the stronger embryo 

 feeding on the weaker one. 



Against Ward's view the developmental evidence seems 

 to point, while by a strict comparison with changes which 

 are known to take place in other sporangia, we are driven to 

 consider the embryo-sac as representing a special-mother-cell, 

 giving rise to two sporocytes, each of which, in their turn, 

 give rise to four spores. 



The eight spores, however, do not behave as normal spores, 

 nor do they seem to have the same sex ; they are neither 

 shed, giving rise to a prothallus and archegonia on germina- 

 tion, as e.g., in Selaginella, nor do they germinate within the 

 sporangium, as in Gymuosperms, where the so-called endo- 

 sperm is in reality a true prothallus forming archegonia. 

 The very fact of eight spores being developed simultaneously 

 in a sac into which nourishment, according to Westermeyer's 

 researches, can only get through the narrow antipodal end, at 

 least in the later stages of its development, and into which, 

 during the earlier stages of development, the nourishment 

 seems, according to ray own observations also to pass through 

 the micropylar end, — nourishment derived in one case through 

 the plerome-elements of the ovule, in the other case from the 

 sister-cells of the embryo-sac undergoing disintegration, — is 

 the reason of the spores occupying the position they do, and 

 not forming a prothallus, but becoming reduced to two 

 synergidal cells, which are two " spores " least developed, and 

 the first to disappear ; — into three sexual cells, one of which, 

 the egg-cell, is fertilised by the product of a pollen-grain, 

 and gives rise to a true embryo, two of which, derived from 



