CELL-FORMATION. 107 



formation in the embryo-sac. Other grounds, however, 

 which exist in the phenomena exhibited in the propaga- 

 tion of the nuclei, render it probable, in my opinion, 

 that the nucleolus originates first, and the nucleus subse- 

 quently, around it.* In that case, those little homogeneous 

 mucilage-globules, first visible, would have to be regarded 

 as the nucleoli. 



At this stage of development we find, as a rule, a 

 homogeneous nucleus inclosing a homogeneous nu- 

 cleolus. Through injurious external influence, a hollow 

 space round the nucleolus is produced. This change oc- 

 curs during the examination. Fig. 9 represents such a 

 nucleus, immediately after the fluid of the embryo-sac 

 had been brought under the microscope. It soon ac- 

 quired the aspect d (fig. 9). This appearance of a hollow 

 space round the nucleolus is observed both when the fluid 

 of the cell is diluted by the addition of water, and when 

 it is brought on the stage without water, and becomes 

 denser through evaporation. The cause of this pheno- 

 menon appears to me to lie in the fact, that through the 

 action of the slightest possible unfavorable influence from 

 without, the mucilage of the nucleus, as well as that of 

 the nucleolus contracts, and they are thus separated from 

 each other. If the action be at all strong, the nucleus 

 and nucleolus contract into a dense, solid body. Care 

 must therefore be taken not to mistake abnormally altered 

 nuclei, such as are drawn in fig. 9, d, for cells with nu- 

 cleus and nucleolus, with which they may very readily be 

 confounded. 



Other nuclei contain two, three, or four nucleoli (fig. 

 7, g \ fig. 8, c\ fig. 9, e). These nucleoli are also some- 

 times of the same consistence as the nucleus, sometimes 

 they are denser, at others not so dense. In abnormal 

 alteration of the nuclei, a hollow space presents itself to 

 notice around each individual nucleolus. Fig. 9, e and/, 

 represent such a nucleus before and after alteration. 



* See the Essay on the Utricular Structures iu the Contents of the 

 Vegetable Cell. 



