Development, and Structure of the Vegetable Cell, 269 



this would be scarcely possible, by reason of the peculiar condi- 

 tions of their development : with others I have performed this 

 task; and respecting the origin of the rest, I have assumed it to 

 be analogous. 



Doubt has been thrown partly upon my observations, and 

 partly upon the conclusions drawn from them. In order to 

 complete the former by a detailed statement of the phenomena 

 which most appeared to stand in opposition to my view, I will 

 here especially demonstrate the free endogenous origin and 

 growth of coric- and pollen-cells, and of the tissue-cells of the 

 simple Algse, which have chiefly been cited as evidence of cell- 

 formation by constriction; and I shall then consider myself 

 justified in assuming that the same law applies also to the origin 

 and growth of other cells. 



By the fuller elaboration and the solution of these questionSi 

 the conviction will be arrived at that the vesicular structure 

 (which takes on at once the character of an active cell, and the 

 properties of which are dependent on the peculiar relative com- 

 position of its formative materials) progresses in a course of 

 development determined by continuous changes in the physical 

 and chemical condition of its membrane and cell-contents, therein 

 resembling the organism at large, in the effectual working of 

 which it has its own part assigned to it. 



By this means physiology will acquire the necessary basis for 

 the right understanding both of the vegetative and animal func- 

 tions of the organism, which it is now attempted to explain, in 

 an equally one-sided and defective fashion, as the action of a few 

 or individual physico-chemical forces governing the evolution of 

 the cell. 



§ I. Development of Cork-cells. 



In Cecropia. — In Philodendron ; in the cells of which they also develope 

 manifold. — Porous, thickened cork-cells. — Restoration of their original 

 spherical form by ammonia.— Absorption of their mother cells. — Growth 

 of a cork-cell out of a cell into the neighbouring vessel. — Cork-cells in 

 crystal-cells. — Cork-cells not developed in lacteal vessels and branched 

 fibrous cells of the bark. — Cork-cells and callus-cells anatomically 

 equivalent. 



The origin of coi'k-cells within those of the epidermis and 

 bark has hitherto been ascribed by the few anatomists who have 

 expressed a definite opinion upon this subject to the sudden 

 appearance of a partition dividing the mother cell into two parts. 

 This opinion has arisen from the circumstance that the investi- 

 gations upon which it is based were made upon the cork-forma- 

 tion of the bark, which does not present a favourable example, 

 as in it the actual moment of the formation of new cells in the 

 bark may easily be missed. 



