Bauhaus-Universität Weimar

Titel:
Microscopical researches into the accordance in the structure and growth of animals and plants
Person:
Schwann, Theodor Schleyden
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit28715/286/
254 
CONTRIBUTIONS TO 
place within the old ones. It is also certain that in this case 
the formative process accords with that above described, B. 
Brown and Meyen have enumerated many instances where 
they observed the cytoblast in very young pollen-cells. In 
PinuSj Abies, Podostemon, Lupinus and others, I have traced 
the development of the pollen after Mirbel perfectly; I have 
distinctly observed the cell-nuclei and their development into 
new cells within one another in Abies, never having missed the 
cytoblast in young cells. 
Now if the pollen-grains be nothing more than converted 
leaf-parenchyma, if the anther be merely a metamorphosis of 
the leaf, we may certainly infer inversely that the process 
which we have observed in it, and which characterized the 
formation of the embryo and cotyledons (as prototypes of the 
leaf) will be again found in all foliaceous organs. For the 
same reason which was stated with respect to the later stages 
of the development of the embryo, actual observation is infi¬ 
nitely difficult in this case. I have nevertheless examined a 
great many buds in reference to this point, and have most 
decidedly convinced myself of the identity of the process both 
in the constantly elongating apex of the axis, and in the leaves 
which always originate somewhat beneath it. Succulent plants, 
the Aloineœ and Crassulaceœ, are best adapted for this purpose. 
Crassula Portulaca seemed to me most advantageous, for in it 
I first succeeded in separating some cells from their connexion, 
in whose interior young cells were already developed, without, 
however, entirely filling the parent-cell. But having once be¬ 
come familiar with the subject, I was afterwards able to detect 
these individualities from amongst the apparently semi-organised 
chaos in all other plants. Another circumstance indeed pre¬ 
sents itself here, which renders the subject much more difficult 
than in the case of the embryo. For, independently of the 
minuteness of the cells, their walls, in those parts of the plant 
which are just newly formed, still consist merely of jelly, and 
are so delicate that it is exceedingly difficult to separate the 
parts intended for examination without completely destroying 
the organization. (Compare plate I, figs. 22-4.) 
This process is more easily perceptible in articulated hairs, 
and in such as have a head consisting of several cells, where 
the same appearances which I have so frequently observed in
        

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