EMBRYOLOGT OF SELAGINELLAE, ETC, 



749 



bosphere ; the suppression of the fertilisation and development of the embryo when 

 the access of antherozoids is prevented, however, is a certain proof of the necessity 

 of the union for the formation of an embryo. 



The processes of reproduction which alone interest us here can be rapidly appre- 

 hended from Fig. 435. /represents a widely open macrospore ; from the aperture 

 through the very thick external spore-membrane, the prothallium d a projects, bearing 

 at a an unfertilised archegonium ; at // is seen a young unfertilised still closed 

 archegonium, in which the lower shaded cell represents the as yet unripe oosphere, 

 and the conical portion lying above it is the canal cell, which, when the neck of the 



Fig. \-i\.—Isoetes laciistris 

 (after Hofmeister). A macrospore 

 a fortnight after sowing, rendered 

 transparent by glycerine (X 60). 

 S longitudinal section of the pro- 

 thallus a month after sowing the 

 spores ; a atcliegonium (X 40). 



FIG. 434, — Selaginella inaequati/alta, 

 A fertile branch {X 2). B longitudinal 

 section of apex oi A, bearing microsporangia 

 to the left and macrosporangia to the right. 



archegonium opens, is extruded as mucilage. /// is the archegonium with a 

 fertilised oosphere already divided by a horizontal wall. While the archegonia are 

 preparing for fertilisation, preparations for the development of the antherozoids are also 

 taking place in the microspores A-D ; after a small cell (w in D) which does not 

 take part in the formation of the antherozoids, has been as it were cut off, further 

 cell-divisions occur in the remaining cells which constitute together, so to speak, a 

 reduced antheridium. This is well seen in D : each of these small cells gives rise to 

 an antherozoid of very simple form, just as in the Mosses. 



Returning to the germinating macrospore again, it is to be noticed that the 



