ZYGOSPORES. 



259 



at right angles to the plane of constriction (/, a) ; in each half-cell are two amylum- 

 bodies and eight chlorophyll-plates, which curve and, running from two centres to the 

 wall, converge in pairs. The multiplication of the cells by division is brought about 

 by the narrowest part of the constriction elongating a little, when the thicker outer 

 layer of the cell-wall opens by a circular fissure ; the two halves of the cell hence appear 

 separated from one another and united by a short canal, the wall of which is a con- 

 tinuation of the inner layer of the walls of the half-cells. A septum soon appears in 

 the canal which unites them, by which the cell is divided into two daughter-cells, each 

 of which is a half of the mother-cell. The septum, at first simple, splits into two 

 lamellae, which immediately become convex towards one another {IX, h), and each 

 daughter-cell now possesses a small rounded outgrowth which grows gradually and 

 assumes the form of a half-cell, so that each daughter-cell now again consists of two 

 symmetrical halves {X). While the wall is undergoing this growth, the chlorophyll- 

 body of the old half-cell grows into the newly-formed half. The two amylum-bodies 

 in the old half-cells elongate, become constricted, and each divides into two; of 

 these four, two pass over into the new growing half-cell, and all again arrange them- 



FlG. XTi.—Cosmarium Botrytis (after De Bary. I— III X 390, IF— A' X 190). 



selves in the original symmetrical manner. Conjugation takes place between cells 

 lying in pairs in a crossed position enclosed in soft jelly (Fig. 171, /). Each of the two 

 cells puts out from its centre a conjugating protuberance (7, c) which meets the other ; 

 these protuberances are formed of a delicate membrane which is a continuation of the 

 inner layer of the cell, the firm outer layer of which is split (7, c). Each of the 

 two protuberances swells up into a hemispherical bladder, they come into contact, 

 the separating wall disappears, and the contents unite in the broad canal thus 

 formed; the protoplasm becomes loosened from the cell-wall, and contracts into a 

 spherical form. The united protoplasmic body appears as if surrounded by a delicate 

 gelatinous wall (77, /) by the side of which lie the empty cell-walls (77, e, b). The 

 zygospore now becomes rounded into a ball ; its wall forms, as it matures, three layers, 

 an outer and an inner colourless layer of cellulose, and a middle firmer brown layer. 

 This stratified cell-wall grows out at several points into spiny protuberances which 

 are at first hollow and afterwards solid, each of them again producing at its end a few 

 smaller teeth (777). The starch-grains of the conjugating cells become transformed into 

 oil in the zygospore. Germination commences by the protrusion of the colourless inner 

 layer through a wide split in the outer layer {IF), the thin-walled ball thus set free 



