l8 MORPHOLOGY OF THE CELL. 



folding-ill of the protoplasmic body makes great progress, pushing on even to the 

 separation into two sacs, before the partition - wall of cellulose begins to form {q 

 and q" in D and E) ; an abnormal condition which shows plainly that it is not the 

 band of cellulose which infolds the sac, but that this latter becomes constricted by a 

 process of growth of its own, which takes place independently of the formation of the 

 partition-wall. The behaviour of the nucleus, and generally the arrangement of the 

 portions of protoplasm during the division, here shows considerable deviation from 

 other similar processes ; this one thing however must be clearly borne in mind, that the 

 formation of two nuclei, and their position in the middle of the newly-formed cells, 

 does not here precede the division, but proceeds along with it. Not till the begin- 

 ning of the infolding which takes place in the circumference of the central nucleus, are 

 two nuclei to be observed in the central mass of protoplasm ; these separate slowly 

 from one another, each surrounded by protoplasm, while the folding-in proceeds, so 

 that, by the time the division is completed, the nuclei have reached nearly the centres 

 of their cells. 



In some cases modes of division occur which appear, at the first glance, to differ 

 essentially from any hitherto described ; e. g. the production of the basidiospores of the 

 Basidiomycetes (as Agaricus, Boletus). A closer study, however, shows that such processes 

 follow more or less exactly one of the types described. Thus, for example, all possible 

 connecting links are to be found between the usual mode of division and the peculiar 

 process in the production of the spores of Agaricus and other Fungi. If the behaviour 

 of the two daughter-cells, rather than the process of division itself, were made the prin- 

 ciple of classification, many other cases would have to be considered. On this I will 

 touch only very briefly. The daughter-cells resulting from the division may be of 

 equal size or not ; in the first case they may be so similar to the mother-cell that they 

 have only to grow in a direction at right angles to that of the division in order to be- 

 come exactly like it (as in Spirogyra) ; but the daughter- cells, even when like one 

 another, may nevertheless be from the first different from the mother-cell ; and this 

 may happen in very different ways, and the difference may constantly increase. But, in 

 other cases where the daughter-cells are from the commencement unlike, this difference 

 usually increases later, especially in the formation of the spores of Fungi on the so-called 

 basidia. A small portion of the end of a long cell becomes divided off; the septum splits 

 into two lamellae, and the separated piece (the basidiospore) falls off; the part which 

 remains attached to the plant shows scarcely any change, and can again and again 

 repeat the same process. The portion of the mother-cell which remains behind, called 

 the basidium, has evidently become a daughter-cell as truly as the detached spore ; but, 

 while the spore is very unlike the mother-cell, the other daughter-cell, the basidium, 

 remains very like it. Hence has arisen the pardonable, but very incorrect expression, 

 that the basidium forms several spores in succession ; whereas properly the formation 

 of each spore is a bipartition, the basidium being always as much a daughter-cell as is 

 the spore (cf. Book II. Fungi). In the same manner the apical cell at the end of a 

 growing stem is the sister-cell to the segment last formed ; but since the former is 

 always renewing itself, it is more convenient to express oneself as if the apical cell 

 always remained the same, and to treat the segments as its products. 



Behaviour of the Nucleus during the Di'vision. Where the cell-division is combined 

 with contraction and rounding off of the newly-formed portions of protoplasm, as in 

 the formation of spores and pollen-grains, it is the rule that the new nuclei become 

 A?isible in the centres of the future daughter-cells, whether, as is usually the case, the 

 nucleus of the mother-cell have previously disappeared, or whether it remain during the 

 process, as in the formation of the spores of Anthoceros (pp. 14-16). From these cases, 

 a clear observation of which was easy, the opinion has hitherto prevailed that in the 

 bipartition of the tissue-cells of growing parts the nucleus of the mother-cell also be- 

 comes absorbed in the protoplasm, and that in this latter two new nuclei arise in the 

 centres of the forming derivative-cells. But the bipartition of the cells of Spirogyra 



