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PHYTOGENESIS. 233 many of the cells in the epidermis of the Orchideæ, an opaque spot, named by him areola, or nucleus of the cell. He subsequently pursued this phenomenon in the earlier stages of the pollen-cells, in the young ovulum, in the tissue of the stigma, not only in the Orchideæ, but also in many other Monocotyledons, and even in some Dicotyledons.

As the constant presence of this areola in the cells of very young embryos and in the newly-formed albumen could not fail to strike me in my extensive investigations into the development of the embryo, it was very natural that the consideration of the various modes of its occurrence should lead to the thought, that this nucleus of the cell must hold some close relation to the development of the cell itself. I consequently directed my attention particularly to this point, and was fortunate enough to see my endeavours crowned with success.

Before, however, I proceed to the communication of these observations, I must first give a somewhat more detailed description of the nucleus. As I have to treat of a peculiar and, I think, universal elementary organ of vegetables, I do not consider it necessary to apologise for applying a definite name to this body, and therefore call it Cytoblast (κυτος, βλαστος) in reference to its function, which will be described hereafter.

This formation varies in its outline from oval to circular, according as the solid which it forms passes from the lenticular into the perfectly spheroidal figure. I have found the oval and flat cytoblasts more frequently in Monocotyledons, in the albumen and pollen; the globular chiefly in the Dicotyledons, and in the leaf, stem, articulated hairs, and similar structures; no exclusive rule, however, can be laid down on this point.

The colour of the cytoblast is in general yellowish, but it sometimes passes into an almost silvery white. I remarked it as being most transparent m the albumen of some water plants, in the unripe pollen, in some Orchideæ, and also in the rudiments of the leaf of Crassula portulaca. Its excessive transparency renders it scarcely perceptible in the spores of some Helvelloids. It is coloured by iodine, according to its various modifications, from a pale yellow to the darkest brown.

It varies considerably in size. It is in general largest in Monocotyledons, and in the albumen; and smallest in