104 Mr. H.J. Carter on the Development of Gonidia 



connected by minute threads of its own material, is drawn back 

 into the internode almost as quickly as it was ejected. 



4<th. By now moistening that part of the internode which is 

 suspended, the mucus is again made to rush forth, and this 

 backward-and-forward movement may be kept up for some time 

 by alternately moistening and allowing the internode to get dry ; 

 or, by keeping the internode constantly moist, the whole of the 

 mucus-contents may at once be discharged. 



Here there is evidently a rapid endosmosis, and it would ap- 

 pear that the mucus-contents, which are within the green layer ^ 

 are not expelled so much by the contraction of the latter, as I 

 had inferred (p. 18), but depend for their exit upon the passage 

 of water through both the cell-wall and the green layer ; while 

 the " spasmodic '^ retraction of the mucus mentioned in the same 

 paragraph must be chiefly attributed to the drying up of the 

 cell-wall, and consequent imbibition through the truncated end 

 of the internode. 



Green layer. — The structure of this has already been described, 

 and the ^'^ green disk^^ was stated to consist of a transparent 

 capsule or cell, within which is a green, flat disk or nucleus, of 

 nearly equal diameter, presenting three or more granules in its 

 composition. It is to the latter now that I chiefly wish to call 

 attention. In these granules I had only been able to obtain a 

 faint trace of starch by iodine, and therefore I left the question 

 of their composition open, although I might have inferred from 

 analogy that they were starch- grains. Subsequent observation 

 has now proved to me that they are the rudiments of starch- 

 grains, and that in some instances where the starch has been fully 

 formed, they have increased to such an extent as to occupy the 

 whole of the transparent capsule (PI. Vlll. fig. 5). Thus packed 

 together of different sizes, they assume the rounded, subangular 

 shapes of all similar bodies developed in a circumscribed space ; 

 at the same time they appear to have been formed at the expense 

 of the green disk, whose substance is much wasted or has entirely 

 disappeared. 



Hence they are generated in the protoplasm of the cell ; for if 

 the green disk be exposed to the action of aether when the gra- 

 nules are very small, the colour of the nucleus disappears, but its 

 form remains ; while at a still earlier period it also appears to 

 contain a nucleolus or cytoblast. Under what circumstances the 

 granules come into existence 1 am ignorant ; but that they have 

 nothing to do with the cytoblast may be inferred from their ap- 

 pearance in the Diatomacese (Navicula fulva, &c.) outside the cell 

 of the cytoblast or nucleus, and in the cavity or body of the 

 frustule, which, up to the time of their appearance together with 

 that of the oil-globules, is perfectly transparent. 



