SCHLEIDEN. 27 



conclusions ultimately come to by Dr. Beale. Schleiden was 

 struck by the observation by Robert Brown, in 1833, of the 

 frequent presence of an opaque spot in the cells of the epi- 

 dermis of the orchideae, which he named the nucleus, but did 

 not follow out the matter further. Schleiden, on the other 

 hand, finding it constantly present in the cells of young em- 

 bryoes, and in the newly-formed albumen, perceived its signifi- 

 cance in the development of the cell, and, finally concluding 

 that it was an universal elementary organ of vegetables, and 

 that by which all cells were formed, named it the cytoblast, or 

 cell bud. The colour of this is yellowish, or white, or at times 

 so transparent that in some plants, e.g., the helvelloids, it is 

 scarcely perceptible from that cause. He observed, also, what 

 had escaped the notice of Eobert Brown, that some contain one 

 or more circular bodies which correspond to what have been 

 since called the nucleoli, and that these were formed earlier 

 than the nuclei, or cytoblast, and can develop into them, and 

 hence into cells. 



In his first description of the formation of cytoblasts he is. 

 not very clear. He states that in the gummy matter from 

 which the tissues of plants are formed a number of granules 

 make their appearance ; and in this mass organization takes 

 place, and a gelatinous matter is formed which is ultimately 

 converted into cellular membrane and fibres. In the above 

 gummy mass, after the granules, cytoblasts make their appear- 

 ance, and when full-sized they form cells, as described thus at 

 p. 238 : " A delicate transparent vesicle rises upon the surface. 

 This is the young cell, which at first represents a very flat seg- 

 ment of a sphere, the plane side of which is formed by the 

 cytoblast." The vesicle gradually expands and increases be- 

 yond the margin of the cytoblast, and quickly becomes so large 

 that the latter at last merely appears as a small body enclosed 

 in one of the side walls between the laminae. " In this situa- 

 tion it passes through the entire vital process of the cell which 

 it has formed" if it be not dissolved and absorbed as a useless 

 member. As a general rule, this last happens ; but there are 

 exceptions in which it remains, such as the orckidece and 

 cactece, which continue through life in a lower stage of develop- 



