Development, and Structure of the Vegetable Cell. 127 



belong exclusively to the cell-nuclei as above described, but that 

 the two large secretion-cells (figs. 61 and 72) may constitute the 

 foundation of the new joint-cells ; in many species these show 

 their relationship to the tissue-cells by their enclosing two large 

 and often many smaller cells. 



These two secretion-cells, which gradually become so much 

 enlarged that at length they fill the whole cavity of the joint- 

 cell (the other equivalent cells diminishing at the same time), 

 consequently represent the two colourless, rapidly enlarging 

 daughter cells, which become developed into new joint-cells, 

 and which, in (Edogonxum, may be recognized as being of this 

 nature by direct observation throughout all their stages of 

 development. 



This, however, has not hitherto been possible in the case c^ 

 the very fragile Spirogyra, and hence we are compelled to com- 

 bine many observations of details in order to obtain a connected 

 picture of their mode of development ; and in this errors are 

 all the more likely to creep in, as the investigation of the de- 

 velopment of the colourless cells in the interior of the joint-cells 

 must be assisted by reagents, the mode of action of which is 

 not yet satisfactorily ascertained. 



Let us first consider those species in the elongated joints of 

 which cell-nuclei are present, but do not appear to produce any 

 daughter cells. If this be really the case, the new joint-cells in 

 these species would be normally formed within the secondary 

 cell of the joint-cell. 



Fig. 74 represents a joint-cell of S. IVeberi, which is divided 

 into two halves by the newly formed, delicate, and still flat 

 septum, whilst the chlorophyll-sac, completely coherent, is still 

 closely applied to the inner surface of the mother cell, as has 

 already been described in S. prmceps. If this condition be 

 observed fur a few hours, we may see distinctly how the sub- 

 stance of the chlorophyll-sac, at its point of contact with the 

 septum, loses its green colour, and finally becomes completely 

 absorbed ; in from four to five hours this process has advanced 

 to the condition represented in fig. 76, in which the chlorophyll- 

 sac is divided into two perfectly separate portions. At this 

 time the septum does not yet exhibit any indication of the 

 annular fold which is subsequently formed. 



No doubt, during this absorption of the secretion-material 

 of the mother cell, corresponding new formations take place in 

 the daughter cells, but these cannot be observed here as in 

 CEdogonium. 



A phenomenon which is probably repeated in most young 

 tissue-cells is, that the organized secretion-materials, and espe- 

 cially the starch and chlorophyll, adhere during their growth to 



