FORMATION OF CELLS. 



^3 



water; and only after they have become fertihsed by the antheridium-tubes («, l? in 

 D) do they surround themselves with a cell-wall. 



This form of cell-dfvision evidently bears, throughout its whole course, a close re- 

 semblance to Free Cell-formation ; it is distinguished only by the circumstance, that here 

 the whole protoplasm collects round several centres. If the whole protoplasmic body, 

 in its contraction, were to form only one ball, which also happens, the case would be 

 analogous to that of Renewal or Rejuvenescence. If the balls, during their separation, 

 were to surround themselves with copiously secreted cellulose, the process would bear a 

 strong similarity to the formation of pollen in many Dicotyledons [see below]. 



There occurs also in this same plant (Fig. 9) a varia- 

 tion of this process of division, when it forms its swarm- 

 spores ; here the protoplasm breaks up in the club-shaped 

 swollen end of a sac into a large number of small portions 

 (yl), which become completely rounded off only (<?) after 

 their escape from the sporangium (B), and are then sur- 

 rounded by a thin membrane which they shortly abandon 

 (Z*) in the process of swarming (e). 



The formation of the spores of Mosses and Vascular 

 Cryptogams, and of the pollen of Phanerogams, always 

 takes place by the division of the mother-cell into four 

 parts, either at once or by repeated bipartition. This 

 is the common character of these formations, which are 

 also otherwise morphologically related. In the special 

 processes of formation, however, some deviations occur ; 

 with the Mosses (e. g. Funaria hygrometrica, see Book II) 

 the formation of spores in the mother-cell follows essen- 

 tially the plan we are here considering ; the protoplasmic 

 body of the mother-cell breaks up into four lumps, 

 which quickly round themselves off and contract, and 

 become enveloped by a cell-membrane only after com- 

 plete separation ; four small cells thus lie encased in the 

 membrane of the mother-cell, just like the oospores 

 of Achlya in the oosporangium, but in this case the 

 mother-cell becomes quickly absorbed. 



The spores of Equisetaceae are formed on the same 

 type ; only the four newly-formed sister-cells (in E. 

 limosiini) do not here lie in a mother-cell-membrane, 

 since the mother-cell does not in general form a 

 cell-membrane before the separation. This case may 

 be examined somewhat more closely, since it brings 

 before us very clearly the behaviour of the nucleus in 

 the division ; and since the behaviour of the other parts 

 is remarkably clear here also. At a certain time the mother-cells of the spores swim in 

 the fluid which fills the cavity of the sporangium ; according to their mode of formation 

 they form groups of two or four sister- cells (Fig. 10, a, b). Each mother-cell consists at 

 first of a large spherical nucleus (including nucleoli), surrounded by fine-grained turbid 

 protoplasm, which has a sharply defined contour, but is without a cell-wall. Dilute 

 alcoholic solution of iodine, and other substances which cause contraction, show this 

 very definitely ; with the contraction of the protoplasmic body of the mother-cell not 

 the very finest trace of membrane becomes visible in any state of division. The first 

 preparation for the division of the mother-cell is manifested by the clarifying of the 

 protoplasm {b), by the gathering of a group of greenish-yellow granules on the 

 side of the nucleus which lies next the sister-cell ; then the nucleus disappears, and the 

 granules arrange themselves in the form of a disc, which passes through the centre of the 



Fig. 9 — Zoosporangiaof an Achlya ( X 550). 

 A still closed, B allowing the zoospores to 

 escape, beneath it a lateral shoot c ; a the 

 zoospores just escaped ; 6 the abandoned 

 membranes of the zoospores which have 

 already swarmed ; e swarming zoospores. 



