334 



you a very brief summary of the more secret part of the 

 process, since our knowledge thereof has been gained entirely 

 by the careful use of the microscope. 



During the maturation of the pollen the stigma becomes 

 enlarged, its central tissue looser, and a viscid secretion 

 bathes its surface, the ovule also alters, for one of its central 

 cells becomes greatly enlarged, so as to form the embryo- sac, 

 and at the end of this sac, next to the micropyle, certain 

 delicate free nucleated cells are produced, which have been 

 termed embryo- vesicles ; and now all is prepared for the 

 crowning purpose of the plant^s existence. 



In Cryptogams, the first sign of a special function in cells 

 is seen in the lower algge, in the process of conjugation, by 

 which a tube is thrown across from adjacent filaments, and 

 the endochrome of one cell passes over into the opposite one 

 and a spore produced in it or in the intermediate tube. 



Passing higher in the scale, we find difierent kinds of 

 reproductive organs : antheridia containing cells with a 

 moving ciliated spermatozoid in each, and archegonia con- 

 taining a germ-cell. In all these cases (Hepaticse, Mosses, 

 and Ferns) the spermatozoids enter the archegonium and 

 reach the central vesicle, which is thus impregnated ; they 

 then lose all motion, and thus precisely correspond with the 

 behaviour of spermatozoa in the animal ovum. 



Taking a Fern as the type, we find the spore grows into a 

 lobulated prothallium, on the under surface of which anthe- 

 ridia and archegonia are produced, the former consisting of 

 a papilla containing free cells which are discharged at an 

 opening in the apex ; these then burst and liberate a ciliated 

 spiral filament, the spermatozoid. The archegonia are fewer 

 and larger, consisting of ten or twelve cells, and have a 

 central canal leading to a large globular germ- cell embedded 

 in the prothallium. The spermatozoids passing down the 

 canal come in contact with the central cell of the arche- 



