64 FERTILIZATION AND FRUIT-FOEMATION IN CKYPTOGAMS. 



water (see fig. 206 0- The spermatozoids then pass through the fissures already 

 described as existing beneath the crown of an amphigonium, and so reach the 

 interior of the latter. Here, in the middle of the cavity is the oogonium (i.e. the 

 great cell containing the ooplasm), and over it there is a slimy gelatinous mass, 

 which occupies more particularly the neck of the amphigonium. The cell-membrane 

 of the oogonium is attenuated and almost liquefied, and these soft and swollen 

 masses of mucilage do not interfere in any way with the progressive motion of the 

 spermatozoids. The latter reach the ooplasm, and, so far as we can see, a coalescence 

 of the two kinds of protoplasm takes place. 



The changes set up in the fruit-rudiment by fertilization first manifest them- 

 selves externally in an alteration in colour. The chlorophyll-bodies, hitherto green, 

 assume a reddish-yellow tint; the spiral cells of the amphigonium become thickened 

 and nearly black, and the amphigonium constitutes a hard shell which acts as an 

 outer envelope inclosing the inner envelope of the fertilized ooplasm, now converted 

 into an embryo. The entire structure next detaches itself from the stalk-cell, sinks 

 under water, and remains for a considerable time — usually through the whole 

 winter — lying unchanged at the bottom of the pond. The embryo does not 

 germinate till the following spring, when it begins by developing a linear series of 

 cells, the so-called pro-embryo, and from one of the cells of this pro-embryo is pro- 

 duced a Stonewort plant with branches in whorls as before (see fig. 206 ^). 



The fruit-rudiment in Muscinese (Mosses and Liverworts) exhibits in many 

 respects a resemblance to that of a Stonewort, although its origin is quite different. 

 It takes its rise from a superficial cell of the Moss-plant, and the cell belongs, 

 according to the species, either to the foliaceous or to the cauline portion of the 

 thallus. This cell projects in the form of a papilla above the adjoining cells, and 

 becomes partitioned by a transverse wall into an under and an upper cell, the 

 former of which serves as a pedestal to the body of tissue developed from the 

 upper cell. The cellular body referred to is differentiated, by repeated insertion 

 of longitudinal and transverse walls, into a central row of cells and an envelope. 

 Amongst the central cells one situated somewhat low down in the series is 

 conspicuous for its size; it contains the ooplasm, and must be looked upon as an 

 oogonium. The central cells, which are placed in succession above it, are called the 

 canal-cells of the neck. The name is derived from the fact that they occupy the 

 constricted portion or neck of the envelope. The cellular envelope, which incloses 

 the central row of cells and constitutes the amphigonium, is shaped like a flask 

 (see fig. 1911"); the lower, enlarged, ventral portion conceals the oogonium, the 

 upper constricted portion is filled up by the neck-cells, and the whole structure, 

 which received from the earlier botanists the name of "archegonium", is closed at 

 the top by a lid composed of several cells. When the time for fertilization arrives 

 the canal-cells of the neck swell up and are converted into mucilage. The lid-cells 

 open and part of the mucilage is forced out; what remains offers no impediment 

 to the admission of the spermatozoids to the ooplasm in the centre of the fruit- 

 rudiment. 



