SKETCH OF MATTHIAS JACOB SCH LEIDEN. 257 



The theory of cells, as given in the " Phytogenesis," may be briefly 

 stated as follows : There are two points in a plant well adapted for a 

 ready and safe observation of the production of a new organization ; 

 these are the embryo-sac and end of the pollen-tube (according to his 

 fertilization theory, the first cells of the embryo should form there, 

 while in reality this is not the case). At both points, the formation of 

 nuclei causes turbidity in the homogeneous gum-solution these in- 

 crease in size, and soon cytoblasts (a granular coagulation) appear. 

 In the free state the cytoblasts increase rapidly until they attain a 

 certain size, when they are surmounted by a fine diaphanous bubble ; 

 this is the young cell, at first a segment of a sphere, its plane side 

 formed by cytoblasts, and its convex side by young cells (the cell- 

 epidermis) similar to a watch-crystal on a watch. Gradually the bubble 

 expands, becomes more consistent, and the wall is composed of cyto- 

 blasts and of a gelatinous substance. The cell grows, overlaps the 

 cytoblasts, and then increases so rapidly that the cytoblast appears as 

 a small nucleus inclosed in a duplicature of the cell-wall. As the 

 growth progresses, the mutual pressure, exerted by the cells upon one 

 another, causes a certain regularity of form, frequently that of the 

 rhombendodecahedron. Only after the resorption of the cytoblasts 

 the formation of secondary deposits begins on the inner surface of 

 the cell-wall. Scbleiden assumes the process thus described to be the 

 general law of formation for the vegetable cell-tissues in the phane- 

 rogams. This theory was conceived while Schwann was still engaged 

 with his theory of the origin and propagation of animal cells. 

 Schwann has, in fact, acknowledged in his " Microscopic Researches " 

 that Scbleiden communicated his observations on the subject to him 

 before publishing them, and thus gave him the light that showed him 

 the way to his own results. So it has come to pass that, by means of 

 the joint labors of these two men, the cell has been recognized as the 

 peculiar element in both kingdoms of organic nature, and all the 

 processes of vegetable and animal life have been located in its little 

 laboratory. 



Schleiden's theory has been proved to be a premature generaliza- 

 tion, based upon incomplete and inaccurate observations, and has been 

 refuted by Nageli ; but, incorrect and of little consequence as it was 

 in itself, it has also proved to be the grain of ferment which has 

 worked a transformation and revivification of biological science. 



Schleiden's theory of fructification was announced just at the time 

 (1839) when those who denied sexuality in plants had seemed to carry 

 the day, and all botanists had agreed, to use the language of M. Her- 

 rera, in attributing the production of the embryo to the ovule, while 

 allowing to the pollen only a simple action of fertilization. " All at 

 once a botanist, already celebrated, proclaimed that he had seen the 

 embryo forming in the grain of pollen and penetrating the ovule with 

 the pollenical tube. This unexpected animalculist was Scbleiden. His 



TOL. XXII. 17 



