GROWTH OF CELLS. 



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cell-membranes are produced around the individualized 

 portion by a new process of formation; the contents 

 secreting organic matter around. When a cell-branch 

 is produced, the individualized portion of contents forms 

 membrane only on its outer face. The growing out of 

 the cell- wall into a branch, however, does not, as I believe, 

 happen through unilateral nutrition, but by a new forma- 

 tion, especially from the fact that the wall of the parent- 

 cell or parent-branch is sometimes already tolerably thick 

 and lamellated before the branch is formed, and because 

 the growing out then assumes an aspect much more as if 

 the membrane of the parent-cell were pushed outward 

 and broken through, than as if it were expanded and 

 formed a branch through nutrition. The origin of a cell- 

 branch is distinguished from the origin of a cell by the 

 fact, that in the former membrane is formed only on one 

 side, in the latter over the whole surface ; and that in 

 the former the production of membrane is continued, in 

 the latter exists but at one short period. The APICAL 

 GROWTH, therefore, like CELL-FORMATION, is connected with 

 a formation of new membrane, but this is unilateral and 

 continuous. 



In cell-formation, as soon as the membrane is formed, 

 it expands by universal growth. In apical growth, as the 

 new membrane is every moment produced, it also at once 

 begins to expand by universal growth. In both cases a 

 thickening of the membrane is combined, at the same 

 time, with the expansion. In both cases, moreover, the 

 expansion only persists for a time, and then ceases. 

 Finally, in both cases, the expansion of the membrane 

 is at all points equal or unequal; in uniform universal 

 growth, the cell or cell-branch is not altered in form ; in 

 irregular universal growth, the cell or cell-branch assumes 

 a shape different from that it originally possesses. As in 

 cell-formation, so also in apical growth, the new formation 

 of membrane and its growth, are only relatively different 

 from each other. Both are conditioned by the secretion 



