FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 49' 



continue to use them with advantage. Thus, under the name of Cryptogam we 

 shall include all plants destitute of flowers in the ordinary sense and possessing 

 organs of fructification which are not clearly visible excepting under the microscope"- 

 whilst the term phanerogam will comprise such plants as bear flowers, and have 

 organs of fructification which are visible without aid from the microscope and are of 

 the nature of metamorphosed leaves. The retention of these old and familiar terms 

 is rendered all the more desirable by the fact that another important distinction, 

 which is inherent in the process of fertilization itself, and has not as yet received 

 sufficient attention, is involved in the separation of Cryptogams and Phanerogams, 

 namely, that in Cryptogams fertilization takes place in water or in a watery- 

 medium, whereas the process in Phanerogams is accomplished almost exclusively in 

 the air. 



FERTILIZATION AND FRUIT-FORMATION IN CRYPTOGAMS. 



In the mountain districts of Central Europe, after the winter snow has melted 

 and the turbid water derived from it has gradually cleared itself up, a beautiful 

 sight is afforded, especially when a ray of sunshine strikes the water, by the dense- 

 crowds of short delicate filaments of a bright emerald-green colour, which every- 

 where form a coating to the stones at the bottom of streams and to the sides of the- 

 troughs used to convey spring-water from the heights. These green threads belong- 

 to a plant named Ulothrix. Each separate filament consists of numerous cells joined 

 together so as to form a chain, as is shown in fig. 201 ^ When these filaments are 

 mature, and the time has come for the production of fruit, the protoplasmic contents- 

 of the separate cells break up into a number of spherical green masses, which, how- 

 ever, continue to be held together in a rounded cluster by means of a colourless 

 substance. An aperture is now formed in the wall of each of the cells in question, 

 and through this opening the conglomerate mass escapes into the surrounding water 

 (see figs. 201 ^ and 201^). The individual masses of protoplasm which compose the con- 

 glq>merate are set free shortly afterwards, and each exhibits at its anterior extremity 

 a pair of revolving cilia, by means of which it swims about in the water (fig. 201 *). 

 When in the course of their peregrinations two protoplasts which originated in 

 one and the same cell-cavity encounter one another they get out of each other's way; 

 if, on the other hand, the protoplasts from cells belonging to different filaments 

 meet, far from avoiding one another, they come into full collision with their anterior 

 ciliated extremities, turn over, and lay themselves side by side and coalesce, f orming- 

 a single body with four cilia (see fig. 201 ^). A little later the cilia vanish, and 

 the product of the coalescence comes to rest. This fusion is the simplest conceivable- 

 case of fertilization in the whole realm of plants. The product of fertilization is. 

 the fruit. It consists in Ulothrix of the little lump of protoplasm formed by the- 

 process of coalescence just described, which now surrounds itself with a thick cell- 

 membrane, and fastens on to some stationary body under water (see fig. 201 ^). We 

 have nothing to do at present with the subsequent development of this fruit ; it is 



VOL. II. 54 



