60 ANATOMY AND PHYSIOLOGY OF 



the formation of a free cell, yet tliis is not a necessary condition, 

 for it appears tliat every globular mass wholly or partly composed 

 of proteine compounds is capable of undertaking the fiinction of 

 a nucleus, clothing itself with a membrane, and thus producing a 

 cell. This state of things is of very frequent occurrence in the 

 formation of the spores of the Algse, where the whole contents of 

 an entire cell, e. g., in Vaucheria, of two copulated cells, e. g,^ in 

 Zygnema, become balled together into a globular mass, and coated 

 by a membrane. But it is not always such large masses, com- 

 posed of starch and chlorophyll granules and protoplasm, which 

 give rise to the formation of a spore ; in very many cases smaller 

 globular masses of the green contents, produced by the union of a 

 a few chlorophyll granules, and undoubtedly also single granules 

 of chlorophyll, may assume this function whence Kiitzing called 

 the granules lying in the cells of Algae — gonidia. This occurs in 

 the most striking manner in Hydrodictyon, in every cell of which 

 the sporidia produced from chlorophyll granules arrange them- 

 selves in a net-work over the whole of the inner surface of the 

 parent-cell, become converted into cells which grow together at 

 their angles, and thus collectively form a new plant. 



Pollen-grains and the spores of the higher Cryptogamia exhibit 

 a peculiar mode of formation which conuects the division of cells 

 with free cell-foimation. After the development of four nuclei, 

 produced by the division of a single nucleus, accompanied simul- 

 taneously by the absorption of that nucleus which had given origin 

 to the parent-cell, the latter becomes divided into four compart- 

 ments (Nageli's special parent-cells) by the folding inward of its 

 primordial utricle and the gradual formation of septa (which are 

 four or six in number, according to the relative position of the 

 nuclei, or, it is first divided into two segments, which are again 

 divided into two chambers (Nageli's special parent-cells of the 

 second degree). These secondary cells are adherent to the wall of 

 the parent-cell wherever in contact with it, therefore up to this 

 epoch only the common process of cell-division occurs (pi. 1, figs 

 8, 9:, 11). But the contents of each one of these four subdivisions 

 now become clothed by a new membrane (the inner pollen or spore- 

 coat), which, although in accurate apposition with the membrane of 

 the cell in the cavity of which it lies, does not adhere to it, and 

 subsequently secretes the outer pollen- or spore-coat. The forma- 

 tion of this inner pollen-cell only resembles free cell-formation in 

 tlie circumstance that its membrane is produced in the cavity of 

 another cell, around a primordial utricle which contains a nucleus, 

 without adhering to the parent-cell and forming one of its secon- 

 dary layers ; it is distiDguished from free cell-formation by the 

 fact that the nucleus and the primordial utricle around which the 

 new cell-coat is produced, belonged previously to the parent-cell, 

 and had caused the origin of this itself, and had not been newly- 

 formed for the secondary cell. 



