FERTILISATION IN MOSSES. 737- 



up to the covering cells w. Fundamentally, however, both together form one row 

 of cells, occupying the axis of the entire archegonium, the protoplasm of which 

 is contracted in the figure and rendered more visible by the mode of preparation. 

 The lowest and largest mass of protoplasm constitutes the still unripe oosphere ; 

 in the central cavity above it lies a smaller cell, the so-called ventral canal-cell, and 

 the narrow neck-canal is still filled up by thin long-drawn masses of protoplasm, the 

 neck canal-cells. When the archegonium is quite ripe, and if water gains access 

 suddenly, the now deliquescent canal-cells swell up strongly and exert a pressure 

 which causes the neck to open at m, the covering cells parting asunder : the 

 mucilaginous substance contained in the canal then escapes, and an open passage is 

 thus formed, at the base of which, in the belly or venter of the archegonium, the 

 now completely developed and spherical oo?phere lies. In this condition fertilisation 

 can take place. 



The antheridia of the male jilant, which have meanwhile become completely 

 developed, are, in the mature condition, sac-like bodies situated on thin pedicles. 

 The wall of the sac consists of a single layer of cells, containing chlorophyll, 

 the colouring matter of which turns red on ripening. The whole of this enclosed 

 cavity is filled with innumerable very minute cells, each of which produces an 

 antherozoid. If the antheridia are completely developed, and a drop of water Hes 

 on the male flower, the antheridia become ruptured at the apex in consequence 

 of its absorption, and, as shown in Fig. 418 A (at a), a dense mucilaginous 

 mass is extruded from the opening, consisting entirely of the mother- cells of the 

 antherozoids, as shown at B, b. By absorption of water these cells swell up, and 

 become isolated, and the antherozoids soon escape from their envelopes and swarm 

 actively in the water. The antherozoids of the Moss are spirally wound filiform 

 bodies thicker at the posterior end, and pointed and provided with two long cilia 

 anteriorly (Fig. 418 ^, c). 



As in all Mosses and Vascular Cryptogams, the archegonia as well as the 

 antheridia open after they have become quite ripe, but only if they are immersed 

 in water. The completion of this process in the case of the Mosses is favoured 

 by their tufted habit : the plantlets stand close together, and when it rains the tufts, 

 with their small interspaces between the leaves, act like a sponge, the male and 

 female flowers become thoroughly wetted, and those archegonia and antheridia 

 which have just become ripe open : the antherozoids now swim about in the 

 water which saturates the tuft of Moss, and some of them occasionally come near 

 the mouth of an archegonium. Then, as if impelled by an attraction exerted by 

 the oosphere and by the mucilage extruded, they collect together at the aperture of 

 the neck, some penetrate by their own movements into the canal, and finally one 

 antherozoid reaches the oosphere, and certainly penetrates into it antl dissolves its 

 substance in it. 



Herewith, then, fertilisation is accomplished, and as usual the immediate efl"ects 

 are that the oosphere excretes a cellulose membrane, and then slowly begins to grow ; 

 this growth is accompanied by corresponding cell-divisions, and thus is produced 

 a multi-cellular embryo (Fig. 419 A,//') in the venter of the archegonium {bb). 

 During the further growth of the embryo, the venter of the archegonium also goes 

 on growing vigorously in comj)anv with it, as may be easily seen from Fig. 419 



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