28 PROTOPLASMIC THEORY BEFORE 1860 SCHLEIDEN. 



ment, and in some other plants, and also in pollen granules. 

 In all this is prefigured the more modern doctrine which makes 

 the nucleus, here alluded to, the truly vital part : but that is 

 not distinctly recognized by Schleiden, although, in the remark 

 which immediately follows, he comes very near to the general 

 principle : " Lastly, many hairs, particularly such as exhibit 

 motions of the sap within their cells, retain the cytoblasts. It 

 is at the same time remarkable, and a proof of the close re- 

 lationship which the cytoblast bears to the whole vital activity 

 of the cell, that the little currents, which frequently cover the 

 entire wall like a network, always proceed from and return to 

 it, and that when in statu integro it is never situated without 

 the currents " (p. 240). 



From the foregoing account of the origin of cytoblasts in the 

 gummy fluid, Schleiden is generally stated to be an advocate 

 for exogenous free cell-formation, and Tyson (p. 33) says, " that 

 it involves a spontaneous generation of the cell." On an atten- 

 tive study of the original memoir on Phytogenesis, this seems 

 to me not borne out, although Schleiden is not so clear as 

 might be wished. For. farther on, he repeats an account of 

 the process, stating that it takes place in the gummy matter 

 within the embryonal cell first, and then in the cells descended 

 from that. The origin of the granules remains doubtful, as from 

 their extreme minuteness, and often transparency, they cannot at 

 first be detected ; and frequently a cell will be found to be 

 absorbed, and two new ones appear in its place, without our 

 being able to detect the stages of the process : and as we know 

 that the smallest nucleolus is capable of becoming a cytoblast, 

 " then indeed we are forced to confess that the imagination 

 obtains ample latitude for the explanation, in every case of the 

 generation of infusorial vegetable structures, even without the 

 aid of a deus ex machind (the generatio spontanea)" He traces 

 the growth of the whole plant to a repetition of what takes 

 place in the growth of the embryo, which consists in the forma- 

 tion of cells within cells. " After the first cells, generally few 

 in number, are formed, they rapidly expand to such an extent 

 that they fill the pollen tube, which soon ceases to be per- 

 ceptible as the original enveloping membrane ; but at the same 



