]n8 R. BRAITHWAITE ON THE HISTOLOGY OF PLANTS. 



also commences by continued separation of cellulose, the extension 

 of the upper daugliter-cell, TvLicli thus gradually attains the length 

 of the lower one. The cellulose case of the mother-cell, following 

 the extension of the daughter-cell, has now become the thin outer 

 case, and the development of the two daughter-cells has reached 

 the point at which we first started. The difference between the 

 cell-division of (Edogonium and the other filiform Algae consists in 

 this, that the mother-cell does not, as in them, before the formation 

 of daughter-cells, extend to double its length ; but in consequence 

 of growth taking place only at its point, the old membrane no 

 longer extensible becomes infolded in the same way as in the for- 

 mation of pores, and the extension of the mother-cell first com- 

 mences when the firm outer case has been ruptured by force of 

 growth, the caps being thus thimble-shaped portions of the cell- 

 case. 



Division in Four. — This proceeds in two ways, the mother-cell 

 either divides into two daughter-cells, each of which repeats the 

 process, or four daughter-cells are at once formed ; the former 

 occurs only in the origin of the mother-cells of pollen in Mono- 

 cotyledons, the latter in that of Dicotyledons, and the spore 

 mother-cell of the higher Cryptogams. The first-named is best 

 seen in the Liliaceee by a section of a very young flower-bud ; at 

 a point of the nucleus, two daughter-cell nuclei appear by division, 

 and this is followed by the lacing in of the primordial membrane, 

 and the division of the cellulose case, so that this is present as a 

 thin membrane soon after the two daughter-cells have become 

 defined, and in them the same process is again repeated. We use 

 solution of sugar or iodine to demonstrate this drawing in of the 

 Primordial utricle in young dividing cells, as the contents become 

 thereby contracted, together with the primordial membrane em- 

 bracing them, while the whole interior of the cellulose case is quite 

 smooth, and without any trace of the formation of transverse walls. 

 When the infolding of the Primordial membrane is farther ad- 

 vanced, we first observe on the inside of the mother cellulose case, 

 the newly separated cellulose case of the daughter-cells. 



The pollen mother-cell of Dicotyledons is best observed in plants 

 with large anthers, as species of Cucurbita, Mallow, or Convol- 

 vulus. In the Gourd or Hollyhock, the primary cellulose wall of 

 the young mother- cell is provided with peculiar hair-like elevations, 

 which gradually disappear as thickening of the coat advances. The 



