Miscellaneous. 381 



existence of two successive generations — one sexual, the other 

 asexual. 



In the Cryptoguraia the phenomenon is easily recognized. Some 

 (Equisetaceae, Ferns, Ophioglosscje) are Isosporece — that is to say, 

 only produce a single kind of spores : these in their turn produce a 

 well-developed prothallium, furnished with chlorophyll and with 

 roots, and consequently capahle of an independent existence. On 

 the same prothallium, or on two neighbouring ones, antheridia first 

 of all originate ; and these, when mature, emit anthcrozoids ; then 

 follow archegonia, generally formed of a central cell to which access 

 is gained by a canal opening outwards. Fecundation effected, the 

 first period is closed ; and then commences the asexual generation. 

 ITie embryo is developed at first in the bosom of the prothallium, 

 but afterwards becomes disengaged from it, and passes through the 

 diff"erent phases of its development, which we have nothing to do 

 with here. Finally, this second generation terminates its evolution 

 by the development of the organs of multiplication, or spores, which 

 always originate from a normal or modified leaf. 



The other Cryptogamia (Rhizocarpeie and Lycopodiaceae) are 

 Heterosporefp — that is to say, provided with two kinds of spores (mi- 

 crospore or androspore, and macrospore or gynospore). Other\\'ise 

 the history of their development may be very easily referred to the 

 plan which we have just sketched. From the two kinds of spores 

 originate prothallia, which are frequently more or less rudimentary. 

 Each prothallium will 2)roduce anthcrozoids or archegonia according 

 to its origin. When fecundation has taken place, the second genera- 

 tion will commence ; the embryo, at first developed in the bosom of 

 the female prothallium, will soon live an independent life, and be- 

 come a complete plant. The evolution, as in the preceding case, 

 will conclude by the development of the spores or organs of multi- 

 plication. 



The Gymnosperms form a very natural transition between the 

 Cryi)togamia and the Phanerogamia properly so called. Xo one will 

 have any difficulty in identifying the anthei-s with the microsporangia 

 and the grains of pollen with the microspores. The cells, from one 

 to three in number, which are always developed in the heart of the 

 anthers, exactly represent the prothallium ; the extreme cell, from 

 which the poDen-tube originates, will be the antheridium. At the 

 point where the pollen-tube applies itself to the ovule, it is often 

 possible to distinguish, in its interior, one or more primordial cells 

 representing the last trace of the mother cells of the anthcrozoids. 



The female organ, rather more profoundly modified, is, neverthe- 

 less, still easy to recognize. The embryonal sac, or macrospore, does 

 not separate from the plant like the macrospores of the Cryptogamia ; 

 the embryo must, in fact, attain a degree of development much 

 higher than in the preceding cases ; it is therefore natural that it 

 should remain adherent to the plant, especially if we consider that 

 the prothallium or endosperm is very slightly developed. 



At the moment of fecundation, or even a little before this, the 

 endospermic cells (prothallium) fill the embryonal sac, or macro- 



