14 



MORPHOLOGY OF THE CELL. 



spherically-formed mother-cell (c) ; the protoplasm thus becomes perfectly free from 

 granules, and as transparent as a drop of oil ; but soon a turbidity again sets in to the right 

 and left of the disc of granules ; fine granules appear at both pdles of the mother-cell, and 



spread further and further, until at last only 

 a clear ellipsoidal space remains right and 

 left (e)', these spots free from granules are 

 two nuclei ; the disc of granules begins to 

 shift its position ; the two large ellipsoidal 

 nuclei again disappear ; and in their place 

 appear four smaller ones (/), arranged in 

 the angles of a tetrahedron, each of which 

 is surrounded on the side facing its neigh- 

 bours by a portion of the greenish-yellow 

 granules which before formed the disc. 

 The optical section soon shows lines which 

 indicate the separation of the four portions 

 of protoplasm (y), commencing internally ; 

 this advances towards the oiltside, while 

 the daughter-cells become globular, and a 

 nucleolus always appears in each of their nu- 

 clei. Finally the young spores become fully 

 isolated (i), adhering only to one another. 

 Here, as in very many other cases of the 

 formation of tetrahedra, preparation is made 

 by a bipartition which is at least indicated 

 (e), but the mother-cell proceeds to a divi- 

 sion into four, even before this first division 

 is completed. The young spores, when first 

 separated, are still naked, but they soon be- 

 come surrounded by a cell-membrane, the 

 peculiar history of whose development we 

 shall investigate at the proper time (Book II. 

 Equisetaceae). 



b. The contracting daughter-cells secrete cel- 

 lulose enjen during their reparation. Since 

 in this case the mother - cell is already 

 clothed with cellulose, the process often 

 gives the impression that the cell-wall of 

 the mother-cell forms at certain spots a 

 projecting ridge on the inside, constricts 

 the protoplasmic body, and at length se- 

 vers it. 



The clearest examples of this case occur 

 in the formation of the pollen of many Dico- 

 tyledons. Fig. 1 1 shows this process in Iro- 

 pcEolum fninus. At a and b four nuclei have 

 already appeared in the protoplasm of the 

 mother-cells which are much thicker on two 

 sides, arranged at the angles of a tetrahedron 

 (this arrangement is common, though not 

 without exception); the protoplasm gives, 

 in fresh examples, the impression of being 

 already divided into four roundish lumps ; but by contraction in an alcoholic solution 

 of iodine (/, g, h, k) it is seen that they are still connected, and that the cell-wall 



Fig. 10. — Mode of formation of the spores of Egnisetmn 

 h'mosutn (XS50) ; a group of four, b group of two uiother- 

 cells ; c and d mother-cells preparing for division ; e one with 

 two nuclei ;y;^ and i division into four spores ; h abnormal 

 fonnation of three spores from one mother-cell. 



Fig. h — Mode of formation of the pollen of Tropaoluvi 

 Wilis (XS50) reduced. 



