106 VEGETABLE CELLS. 



mucilage exhibits an equal density up to the border of the 

 drop of water, so that where the water commences the 

 mucilage appears as if cut off from it. Sometimes it is 

 denser at the borders of the drop of water, and seems to 

 form a proper membrane around it. Probably this is the 

 consequence of a lengthened action of the water upon the 

 mucilage. In any case the watery vesicles go no further ; 

 certainly undergo no organic changes. 



All perfect nuclei lying in the fluid must also be ex- 

 cluded in the consideration of cell-formation. They are 

 wholly absent at first, and multiply in proportion to the 

 number of fully-developed endosperm-cells contained in 

 the embryo-sac. They are the nuclei of these cells, and 

 become free, with the granular contents, through their 

 destruction. These nuclei are very apt to lead the ob- 

 server astray, since they are not capable of the subsequent 

 stages of development. 



Small, globular drops of perfectly homogeneous mucilage, 

 with defined outline, are absolutely constant phenomena in 

 the process of cell-formation in the embryo-sac. They 

 vary from '001 -'004 of a line, and are distinguished from 

 the mucilage-granules, even in the earliest condition, 

 by a perfectly globular form and smooth surface. The 

 mucilage-globules are never absent ; they always con- 

 stitute the first stage of cell-formation (pi. II, fig. 7, a, 

 b, c; 8, a). They exactly resemble the mucilage-globules 

 which represent the nascent germ-cells in Valonia and 

 other Algae, in Lichens and Fungi. 



A more advanced stage is represented by the larger 

 mucilage-globules, in which a smallish ring is inclosed, 

 ivhile the whole olobule possesses an uniform consistence 



/ JL */ 



(fig. 7, d, e, /). The inclosed ring may appear clearer 

 (fig. 9, a] or denser (fig. 9, b) than the outer part of the 

 globule. There can be no doubt, and the further deve- 

 lopment also confirms it, that the mucilage-globule is a 

 cell-nucleus, the inclosed ring a nucleolus. How have 

 the nucleus and nucleolus originated ? This is a question 

 which I cannot answer from direct observation on cell- 



