the Development of the Organic Cell. 11 



probably also from this same defect in the supply of nitrogenous 

 substance from without, was absorbed by the more actively 

 assimilating membrane of the fold. 



In S. nitida I have observed such cii'cular folds for fourteen 

 days together, without being able to detect a further enlarge- 

 ment of them ; and I can give so much the less credence to 

 the hypothesis that septa and cells originate from these folds, as 

 I have noticed similar circular folds in Cladophora glomerata 

 lasting for a period of three months without any change in their 

 central aperture taking place. 



Further, I have not only observed, in Cladophora, the new 

 joint-cells, in certain exceptional cases, take on such a develop- 

 ment as to present two free endogenous cells dividing in the 

 cavity of the mother cell (as in cork-cells, in Spirogyj-a, and 

 (Edogonium: see my 'Histological Researches,' figs. 21-29), 

 but I have also seen, in the plant in question, that the thick 

 membranous folds intervening between the two daughter cells 

 grow gradually thinner and become finally absorbed. In Sph'o- 

 gyra, moreover, I have also witnessed the absorption of the 

 membrane of the secondary mother cell, which has subsided, 

 along with the chlorophyll-vesicles connected with it, towards 

 the conjoined ends of two slowly growing joint-cells, and has 

 there become included in the septum produced, and assumed 

 the form of an elevation or fold. (Histological Researches, 

 p. 63.) 



From the analogy of these occurrences, it may be assumed 

 that even the folds represented in figs. 12 and 14 would become 

 absorbed by the neighbouring cells, if these last were restored 

 to a vigorous and normal state of nutrition, which might in all 

 probability be eflfected, where atrophy had not too far advanced, 

 by the cautious supply of organic nutritive matter. 



Fig. 19 exhibits a specimen of Cladophora glomerata, in which 

 one of the two daughter cells, during the absorption of the 

 secreted matters by the fold, has penetrated this last in the 

 course of its growth, come into contact with its sister cell, and 

 thus established a new septum. 



In the same plant (fig. 18) a thick fold has formed a boundary 

 between the two new daughter cells, and so created an obstacle 

 to their coming into apposition. In the centre of the fold a 

 large corpuscle, like a starch-globule, remains unabsorbed by 

 the daughter cells which did not touch it. It would seem that, 

 in this example, the very thick circular fold of the mother cell 

 has prevented the formation of a septum by the daughter cells. 



A careful examination of Cladophora is sufficient to convince 

 any one who might regard an appeal to analogy, even in allied 

 plants, as inadmissible, that though an endogenous cell-growth 



