22 SURVEY OF THE REPRODUCTIVE PROCESS 



higher or phanerogamic plants, which constitute the vast 

 majority of the present flora of the world. The ovule is a 

 cellular body containing the germ, and developed from a 

 peculiarly modified leaf or carpel, which in the Coniferse 

 leaves it quite exposed, but in by far the greater number 

 of plants is wrapped round it to form the germen or ovary. 

 The pollen grains are secondary cells developed in an 

 anther or terminal appendage of a stamen representing 

 the lamina of a peculiarly modified leaf and are set free 

 by the dehiscence of its exterior envelope. They have the 

 property, when brought in contact with the ovule or the 

 stigmatic surface of the ovary, of emitting, through valvular 

 openings in their outer coat, long tubes produced by the 

 outgrowth of the contents and inner wall. The pollen tube 

 passing through the tissue of the style or neck of the ovary 

 to the ovule or, when this exposed, entering its micropyle 

 directly comes into that relation with the included ger- 

 minal corpuscule, which is necesssry to its fertilization. 



With these preliminary remarks on the general relations 

 of the reproductive process in the vegetable kingdom, we 

 may now proceed to a summary of the most important mo- 

 difications of its details in the principal groups, commencing 

 with the simpler cellular forms. 



REPRODUCTION IN THE PROTOPHYTA. 



Under this head I propose to consider the process in 

 some of the simpler Algse, which I take by themselves simply 

 for convenience sake, and without hazarding any opinion on 

 the value or limits of the group. The term, I think, is 

 generally employed in this indefinite way, and it is, there- 

 fore, to be regretted that its etymology should suggest a 

 parallelism to that of Protozoa, a very natural primary 

 division of the animal kingdom. 



I confine myself, then, in this section to Algae of those 



