i6 



MORPHOLOGY OF THE CELL. 



protoplasmic contents of the mother-cell has already become divided after the disappear- 

 ance of its nucleus ; the protoplasm has collected round two nuclei which lie in the foci 

 of the nearly elliptical figure of the mother-cell in such a manner that a translucent 

 plane at right angles to the line of union of the nuclei indicates the separation. The next 

 condition to be observed is always that represented in //, where a lamella of cell-wall 

 completely divides the mother-cell, lying in the translucent plane already indicated in /. 

 The place where the wall of the mother-cell and the partition-wall meet soon becomes 

 thicker, and the two daughter-cells here become rounded off. The two nuclei in // are 

 elongated, corresponding to the form of their cells ; they soon become absorbed (///), 

 and in their place two new nuclei immediately arise in each half-cell (/^), whose position 

 again corresponds to the foci of the elliptical daughter-cells. Sometimes this preparation 

 for division remains uncompleted in one of the two cells (^). Between each pair of 

 tertiary nuclei a division-wall now suddenly arises (^i). Now for the first time the 

 nucleus of each young pollen-grain is further developed ; it becomes transparent, and 

 a nucleolus can now be recognised. In the formation of pollen of Dicotyledons the 

 further process is so far the same, that the common cell-wall softens (at first on 

 the inside, FIl, x'), and is at last absorbed, while a new and firmer membrane is formed 

 around each derivative cell. 



In this case I was unable to separate the two halves of the protoplasmic body (7) 

 by contraction \ With the formation of the pollen of Ganna I was successful, only 



however when the second 

 division had already be- 

 gun; four masses of proto- 

 plasm are then seen com- 

 pletely separated ; they are 

 not rounded, but formed 

 as if the body of the 

 mother-cell had been di- 

 vided by two cuts; the 

 division-walls then appear 

 suddenly between these 

 primordial cells. In a 

 similar manner the at- 

 tempt has also sometimes 

 been successful, in the 

 formation of tissue-cells, 

 to separate the two 

 daughter-cells completely by contractile reagents, before a division-wall has arisen be- 

 tween them : as also in the first divisions of the young antheridium of Gharaceae 

 (Fig. 43, B). But usually, especially in the formation of the tissues of the higher 

 plants, the appearance of the division-wall follows so rapidly after that of the two 

 nuclei, that it is seldom possible to catch the exact moment when the deriva- 

 tive cells are already parted, but are not yet separated by a partition-wall. In the 

 examination of -the Punctum i>egetationis of roots and stems, one sees at a glance 

 hundreds of cells which are in process of division at the same time ; and yet it is 

 seldom possible to see the condition in question. This however shows at the same 

 time that the partition-wall always arises in these cases simultaneously over the 

 whole surface ; if it grew from without inwards, this would actually be seen, since 



Fig. 13. — Formation of tlie anthericlium n{ Nitella flexilis (cf. Book II). 



^ The firm connexion of the two daughter-cells before the formation of the partition-wall 

 occurs also in a different manner, e.g. in Oedogonium (Hofmeister, I.e. pp. 84 and 162). The 

 preliminary indication of the partition-wall by the appearance of a disc of granules in the boundary 

 plane is not universal, as is shown in the formation of the pollen of Funkia and of the spores of 

 Funaria. (Hofmeister, /. c. Fig. 20.) 



