REPRODUCTION OF MARSILIA. 



747 



they move forwards, their spirals rotating : as in many other cases a delicate vesicle 

 clinging to their hinder end is carried with thern (Fig. 431). 



In the narrower end of the very large macrospore, which is filled with starch- 

 grains and invested with a very thick firm membrane, the first rudiment of the 

 prothallus arises undef the' apex by the collection and rapid division of a mass of 

 protoplasm. Thus the prothallium is incepted 

 in the interior of the spore : it is separated off 

 from the remaining (far larger) cavity of the spore, 

 by means of a transverse wall, the diaphragm. 

 Then the apex of the spore opens, and as the 

 diaphragm protrudes beyond the opening as a 

 vesicle, the young prothallium is , forced out of the 

 spore-cavity, and thus comes into the lower part 

 of the so-called ' funnel,' which is formed by a trans- 

 lucent soft gelatinous mass situated at the anterior 

 end of the macrospore ; a funnel-shaped canal in 

 this gelatinous mass leads down to the prothallium. 

 The latter is, however, very small in comparison 

 with the very large macrospore, and from its whole 

 cell-structure it may be looked upon as practically 

 a single archegonium. 



On allowing the sporocarp of a Marsilia to 

 open in a glass of water, the stages of development 

 of the macro- and micro-spores described may be ob- 

 tained after from ten to fifteen hours, the temperature 

 being suitable. The water ssvarms with thousands 

 of the rapidly moving antherozoids, hundreds of 

 which now crowd into the funnel-opening of the 

 macrospore, while others bore directly through the 

 soft jelly ; some of them reach the naked oosphere 

 lying in the venter of the archegonium, from which 

 in the course of two days an embryo like that in 

 Fig. 432 is then developed, which already possesses 

 the first leaf b, the apical-cell of the shoot-axis s, 

 the primary root w, and the so-called foot/I By 

 means of this foot f the embryo is attached to 

 the protruding vesicle of the macrospore c, and is 

 nourished by the latter. The whole structure at 

 this stage is strikingly suggestive of the develop- 

 ment of a Fish still bearing the yolk-sac at its ventral surface. As in the Mosses 

 and Ferns, so also here the archegonium goes on growing for some time longer, 

 and appears in the figure as an envelope consisting of two cells and investing the 

 embryo, the neck portion of the archegonium {a) being still quite evident. From 

 the lower part of the archegonium or prothallus (/ /) numerous long root-hairs 

 grow out (wA) by means of which the whole structure is anchored firmly at the 

 bottom of the watfer; since it is one of the first objects of every embryo-plant to 



FIG. 431..— J/arji/ia salvatrix. Upper 

 figure, Macrospore sp with gelatmous en- 

 velope si, and apical papilla protruding 

 into the funnel. In the papilla is a flattened 

 yellow drop ; sg ruptured wall of macro- 

 sporangium (X about 30). Lower figure, 

 ruptured microspore aft^r the escape of 

 the antherozoids : ex epispore ; dl extruded 

 endospore, containing granules ; z z spiral 

 antherozoids; yy their vesicles, contain- 

 ing starchy granules. The gelatinous en- 

 velope of the microspore has disappeared. 

 The protuberances on the exospore are 

 wrongly represented (X 550). 



