THE VEGETABLE CELL. 59 



cl&cidcdly false, foi^ all recent observations agree in diewing tliat the em- 

 biyo originates from the germinal vesicle by cell-division ; not less incor- 

 rect is it, that free cell-formation may be traced in jointed hairs, and just 

 as little does it accord with the mode of formation of other plants that, as 

 is stated (^' Grundz.'' L 211), cells are formed in cells, and the parent-cells 

 absorbed, hi the i)oints of the roots and shoots of the stem of Gypri^n- 

 cl'mm. The entire representation proves that Sclileiden has never once 

 observed the division of a cell. 



The first account given by Sclileiden (" Beitr. zur Fhytogenesis^ MuUer's 

 Archive 1818) of the process of cell-formation, was faulty m many re- 

 spects. He altogether overlooked the important ckcumstance that the 

 nitrogenous substances were the originators of the formation of the 

 nuclei and the cell, for he believed the granules of protoplasm, which 

 he denominated mucilage {schhim)^ to be identical with the granules of 

 gum, and thought that the protoplasm might be replaced by starch, and 

 go through similar metamorphoses ; for he expressly mentions that starch, 

 or the granular mucilage replacing it, is present in the pollen-tubes, but 

 those substances are soon dissolved or change into sugar or gum. In the 

 formation of a nucleus those httle mucilaguious granules were produced 

 in the protoplasm, then a few larger granules, and soon afterwards the 

 nuclei shewed themselves. When a cell was foimed, it had at first the 

 form of a segment of a sphere, the plane side formed by the cytoblast, the 

 convex side by the cell-membrane. Originally the cell-membrane was 

 soluble in water, but it soon expanded more and more, and acquired 

 greater consistence ; and its walls, with the exception of the cytoblast, 

 which always foi-med part of the wall, were composed of gelatine. The cell 

 now bOon became so large that the cjrfcoblast appeared oiiLy as a little body 

 enclosed in the lateral wall. The cytoblast might go through the whole 

 vital process with a cell, if it were not dissolved and absorbed in cells des- 

 trued to higher development, either in its place or affcer it has been cast 

 off like an useless member, in the cavity of the cell. — The whole of this 

 account of the relation of the nucleus to the cell-membrane is incorrect. 

 The nucleus is not connected with the cell-membrane under any circum- 

 stances, for it is enclosed, with all the rest of the contents of the cell, in 

 the piimordial utricle. Its position in the newly originatiug cell is, as 

 appearb to me, always central, and its form mostly globular ^ it does cer- 

 tainly often lie upon the wall of the cell subsequently, and becomes fiat- 

 tened. The distinction which iJTageli tries to carry out between central 

 and parietal nuclei is not founded in nature. 



In Schleiden's more recent writings the above views are partially modi- 

 fied. It has been recognized that the supposed gum is a nitrogenous 

 substance, but the name mucilage (schleim) has been retained ; and it is 

 stated of the young cell, that in many cases, after one side of it had become 

 elevated like a vesicle from the surface of the nucleus, a second layer is 

 deposited upon the free side of the latter, protecting it from solution ; the 

 special statement that all cells are formed in this way is more and more 

 extended to aU organs of plants, even to the cambium-layer of the Dico- 

 tyledons (" Anatomie der Cacteen,'' 35). 



Although it is a rule, which has no exception in the normal 

 development of the cells of all the higher plants, that nuclei make 

 their appearance in the nitrogenous substances which give rise to 



