YESTERDAY AND TO-DAY 27 



of the Flowering Plants is the Gymnosperma 

 (which includes the Conifers), and it is interesting 

 to note the points of similarity between a typical 

 Gymnosperm and a Selaginella. To start away 

 with, the Selaginella bears two kinds of spores, 

 each of which in its development has a definite 

 sex character. The smaller ones (microspores) 

 are in their manner of production analogous to 

 the pollen-grains of the Flowering Plant. The 

 prothallus and the male organ (antheridium) 

 are comparable to the special cell-group in the 

 pollen-grain, whilst the spermatozoids approxi- 

 mate to the generative cells. In the larger spores 

 (megaspores) these represent the embryo sac, 

 and the sporangium in which they are produced 

 closely approximates to the part containing the 

 embryo sac in the Flowering Plant. The pro- 

 thallus which arises from the megaspore in the 

 Selaginella closely resembles the endosperm a 

 special tissue formed to feed the embryo in the 

 case of flowering plants. The female organ 

 (archegonium) and the cell which it produces are 

 practically identical in both cases. Fossil re- 

 mains have shown that some of the plants like 

 Selaginella which flourished in Palaeozoic times 

 seemed to have come very near to the production 

 of seed. Thus one species which has been 

 described shows a megaspore which was per- 

 manently within the sporangium, and which in 

 its general development greatly resembled a 

 fruit. It is, of course, impossible to give more 

 than a very brief outline of some of the chief 

 points in this highly important comparison 

 between the Gymnosperm and the Selaginella. 

 The author trusts that those of his readers who 

 are interested will pursue the study in the ad- 

 mirable textbooks which are now available. 

 The Horsetails, like the Club Mosses, have had 



