26 ORaANOGRAPHY 



by the action of carmine, as just noticed in reference to proto- 

 i plasm. Mohl, who first discovered this structure, and who believed 

 it to possess all the characters of an inner cell lining the outer 

 one, called it the Primordial Utricle, from the fact of its existing 

 previous to the cell- wall formed of cellulose. By some observers. 

 as already noticed (see page 18 _K the primordial utricle is re- 

 'garde(it as a' portion of the c eTTwall, and not as one of the 

 contents ot tne cell. Whether such an appearance as that just 

 d'escribed, can be considered as owing to the presence of a distinct 

 membrane having the characters of an inner cell, as supposed by 

 jMohl ; or whether it should not be rather regarded as due to a 

 I film caused by the coagulation of the surface of the protoplasm 

 *l)y the action of the reagents applied, is by no means clear, for 

 bwhen a cell containing protoplasm is examined without the aid 

 I of reagents, no membrane thus bounding the contents of the cell 

 [lean be clearly distinguished. It^ wo uld appear, therefore ^ far 

 more probable that this jio-called primo rdial iitricle is nlerely a " 

 tETfi^enecTlayer of T he protoplas m lining the cellulose-walTT ' 

 whichna s ass umed t he c h aracter of a true membrane uii der the 

 action or~rea gents, ju st in the same way as any~l Eckened_ 

 gelatinous matter, when exposed to tde air, would become m^ 

 vest^cT as it'dri ed up by a inofe~or less evident p ellicle. This 

 tEickened layer of protoplasm, or primordial utricle, ^rforms, 

 as we shall afterwards find, a very important part in the pro- 

 cess of cell-development ; it may be, therefore, always observed 

 in young and vitally active cells. Its existence is in most 

 cases but transitory, disappearing when the secondary layers are 

 being deposited. It is^Jiowever, a permane nt formation i ii_cell_ s 

 c ontaining cHTorophyll (the green colouring 

 9- ^^' matter of plants), as, for in stance, in the cell s 

 of. leaves^_andi__iii man y o f the lowi ^ kinds "of 

 plants. 



Nucleus or Cytohlast . — Almost all young cells 

 contain one or more bodies called Nuclei or 

 Ci/tohlasts, wh ich are alway s in intimate con- 

 nexion with flie prim ordial utricle. In the 

 cells of the more highly organized plants the 

 nueleiis consists of a rounded or lenticular 

 Fig.^x. Cell with gi'amdar-looking body {figs. 24 and 51), which 

 nucleus aud uu- is genei'ally more transparent than the pro- 

 '^'''^'"®- toplasm in which it is placed, and containing 



almost invariably in its interior one or moi-e usually sharply 

 defined bright points called Nucleoli {fig. 51). These nucleoli 

 vary somewhat in their appearance ; more commonly they seem 

 to be formed of solid transparent granules, while in other cases' 

 they appear like small cavities in the interior of the nucleus. 

 Nuclei are generally regarded as solid granu.lar structures ; but 

 Nageli and others describe them as vesicles. The nucleus and 



Wm^^mt- 



