R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 1G5 



wliich consume the whole contents of the mother-cell during their 

 development ; and the same is seen in zoospores of many filamentous 

 A]gdd and Fungi {Feronospoixi, Saprolegnia, &c.). 



After the destruction of the nucleus of the mother-cell, we 

 observe as many nuclei as there are daughter-cells developed. 

 Eound. each of these is collected a denser mass of protoplasm, 

 which becomes invested by the primordial membrane, and then by 

 the cellulose case, and thus the new cells are complete. In the 

 resting spores of Fungi, according to recent observation, a previous 

 impregnation is necessary to originate the cellulose case, just as in 

 the embryo- cell of higher plants. 



The rapidity with which cells often multiply is truly marvellous ; 

 thus in that great Puff-ball Bovista giganteum, which we frequently 

 find bigger than a hat, it has been calculated that 20,000 new cells 

 are formed every minute, and Kieser estimates the tissue of some 

 fungi to increase at the rate of 60,000 per minute. The sudden 

 appearance of large tracts of water discoloured by minute Algse is 

 also thus readily explicable. 



2. Cell Formation by Division. — Here the contents of the 

 mother-cell, by a contraction or lacing-in of the cell-membrane, are 

 divided into as many parts as there are new daughter-cells, and this 

 process also offers two types. In one we have complete division of 

 the living cell, i.e., the membrane and contents, along with simul- 

 taneous division of the cellulose case ; in the other, during the ad- 

 vancing contraction of the primordial membrane of the mother- 

 cell, the division of the cellulose case occurs subsequently. In the 

 first group a bipartite division only has been observed, but in the 

 second both 2 and 4 parting occur. Bipartition, with subsequent 

 formation of the case round two daughter- cells, is best seen in the 

 filamentous Alg^, and the multicellular hairs of Pheenogamous 

 plants ; whilst the origin of 4 daughter- cells may be observed in 

 the formation of the mother-cells of spores and of pollen. 



Cell Division, with Simultaneous Division of the Cell-case may be 

 observed in higher plants, in the parenchyma of the growing point, 

 in formative tissue, and in the advancing development of the 

 albumen of the seeds of phgenogamous plants ; the observation is 

 however, difficult on account of the obscurity of the cell contents 

 but is most readily seen in the wide celled root-wood of Conifers. 

 The new cambial growth takes place later in the root than in the 

 stem and branches, so that if early in summer we take thin 



