THE CELL DOCTRINE. 31 



ployed in new formations, it becomes dissolved into 

 sugar or gum, which are convertible into one another. 

 The sugar appears as a perfectly transparent fluid, 

 not rendered turbid by alcohol, and receiving from 

 tincture of iodine only so much color as corresponds 

 to the strength of the solution. The gum is some- 

 what yellowish, more consistent, less transparent, 

 and coagulated into granules by tincture of iodine, 

 assuming a pale yellow color which is permanent. 

 In further progress of organization, in which the 

 gum is always the last fluid, a quantity of exceed- 

 ingly minute granules appears in it, most of which, 

 from their exceeding minuteness, appearing as black 

 points. Here it is that organization takes place, 

 though the youngest structures are composed of 

 another distinct homogeneous, perfectly transpa- 

 rent substance so transparent as to be invisible 

 when not surrounded by opaque or colored bodies, 

 and continuing thus after pressure. This he calls 

 vegetable gelatine, and considers as slight modifica- 

 tions, pectin, the basis of gum tragacanth, and many 

 of the substances usually enumerated under the term 

 vegetable mucus. It is this gelatine which is ulti- 

 mately, through the agency of the nucleus, converted 

 into the actual cell-wall, or structures which consist 

 of it in a thickened state, and into the matter of 

 vegetable fibre. 



In this homogeneous blastema or cytoblastema (said 

 to be most easily studied in the embryo sac, and in the 

 extremity of the pollen tube), are very soon precipi- 

 tated or developed mucous or protein granules, when 

 the solution immediately becomes cloudy and more 



