418 Prof. H. Karsten on the Formation, 



until they assume polyhedral forms, which occupy the central 

 space of the joint-cells — are seen (as in fig. 31 x) pushing for- 

 wards beneath the cells filled with chlorophyll which occur on 

 the surface. 



During the period of the multiplication of the joint-cells, 

 either the larger of these endogenous cells filled with secretory 

 matter are, as it would seem, entirely absent, or else those are 

 chiefly present which enclose in their readily soluble membranes 

 the smaller ones containing chlorophyll and starch. These can 

 then only be recognized in the vicinity of large endogenous cells 

 which are no doubt developed into new joint-cells. 



The relative proportion in which these two forms of endo- 

 genous cells are present, and their consequent position in the 

 joint-cell of the Confervse, cause the wide range in form which 

 prevails in these plants. 



As the mode of development and distribution of the endo- 

 genous cells is dependent upon the nutrition of the plant, and 

 consequently upon the chemical composition of the fluid in which 

 it grows, the cultivation of Cladophora glomerata will furnish 

 important materials for a revision of the systematic value of 

 those forms. 



The great tendency to the diff"usion of fluid which the trans- 

 parent cells exhibit causes these cells, when the uninjured plant 

 is placed in a solution of tannic acid, to expand greatly and to 

 become visible on the surface after some time has been allowed 

 for the reagent to act. This reagent will frequently bring to 

 light the presence of cells within joint-cells, even although be- 

 fore quite invisible, the whole substance looking like an unor- 

 ganized mucilage. This is well seen in the case of the colourless 

 contents of the joint-cells of Mougeotia, in the median line of 

 which the single mass of chlorophyll appears to float freely, 

 surrounded by a colourless homogeneous fluid. This latter, 

 however, is found to consist of a mass of closely placed, rather 

 elongated, or often somewhat cubical cells, by the expansion of 

 which in a spiral direction the twisted form which the chloro- 

 phyll often exhibits is produced. 



These cells likewise usually become very distinct in the joint- 

 cells undergoing enlargement alongside wounded joint-cells, after 

 they have remained for some time in pure water, and thus give 

 the surface of the plant a largely cellular reticulate aspect. 



In PI. VI. fig. 39, an instance is figured of the expansion of 

 one of these endogenous cells to half the dimensions of the 

 joint-cell, without having new cells formed within its cavity. 



The great delicacy of the walls of the endogenously stratified 

 (nested) system of these cells is an obstacle to the recognition 

 of the plan of their arrangement and of the course of their de- 



