32 



MORPHOLOGY OF THE CELL. 



organisation' in the same sense we speak of as 'water of crystallisation ;' and as the latter 

 is indispensable to the formation of many crystals, so is the former to the structure of 



the cell- wall. It is 

 moreover, as we 

 shall see, a peculi- 

 arity of all organ- 

 ised structures, that 

 they contain ' water 

 of organisation,' at 

 least as long as they 

 grow, because they 

 all alike grow by- 

 intussusception. 



From what has 

 been said, it can 

 easily be seen that 

 the concentric for- 

 mation of layers of 

 a cell-wall growing 

 by intussusception 

 essentially differs 

 from the repeated 

 formation of cell- 

 wall round one and 

 the same proto- 



FlG. 35.— Macrospores oi Pilnlaria ^lobidifei-a, in optical longitudinal section ; to the left a still 

 unripe spore, in which the outermost gelatinous layer of the cell-wall is still wanting, which is 

 present in the ripe spore to the right ; the two outermost layers of the cell-wall of the latter 

 (c and d) have assumed a prismatic structure, which is especially clearly manifest at <r ; at rf 

 stratification is feebly indicated at the same time. Seen from the surface the prisms appear like 

 areolae ; the boundary surfaces of the prisms are, in the corresponding cell-wall-layer of Marsilea 

 sahuitrix, more solid and cuticularised, by which the appearance of a honey-comb is obtained. 

 (Cf. J. Hanstein, Berliner Monatsbericht ; Feb. 6, 1862, Fig. 17, and Book II. Rhizocarpew.) 



plasmic body ; cell- 

 walls enclosed one within another may be produced in this manner ; these, however, 

 must not be considered as layers of one cell -wall. This process is very common 



in the formation of the pollen-grains of 



^'^.<^^?^- 



Phanerogams ; within that mass of cell- 

 wall-layers which forms what is usually 

 designated the special mother-cells, each 

 protoplasmic body forms round itself a 

 new cell-wall, before the mother-cell-wall 

 is destroyed (Fig. 36). 



But the renewal of a cell-wall may also 

 be brought about by the external mass 

 of layers undergoing no further growth, 

 while the internal layers of the same 

 cell - wall increase by intussusception. 

 Thus the cell-wall of spores and pollen- 

 grains is origiuc^ly a whole increasing by 

 deposit ; by subsequent internal differ- 

 entiation masses of layers are formed 

 differing in their chemical and physical 

 properties ; the outer firm cuticle (ex- 

 ospore, extine) remains subsequently 

 unchanged : it is thrown off as an en- 

 velope, while an inner mass of layers 

 (the endospore in one, the intine in 

 the other case) begins a new growth 

 with the germination of the spores and 

 pollen-grains. A similar process occurs 

 with many filamentous Algae (Rivularieae and Scytonemeas), where a large number 



Fig. 36.— Pollen-mother-cell of C2<cz^;-*z?a/'^/<?; j^the externa 

 common layers of the mother-cell in the act of absorption ; sp the 

 so-called special mother-cells, consisting of masses' of layers of 

 the mother-cell which surround the young pollen-cells ; they also 

 are afterwards absorbed ; ph the wall of the pollen-cell ; its 

 spines grow outwards and penetrate the special mother-cell ; 

 "v hemispherical deposition of cellulose on the pollen-cell-wall, 

 from which the pollen-tubes are afterwards formed ; / the con- 

 tracted protoplasmic body of the pollen-cell (the preparation was 

 obtained by dissection of an anther which had lain for some 

 months in absolute alcohol (X5S0). 



