28 Prof. H. Karsten on the Formation, 



turn from beneath the chlorophyll-bands, which previously con- 

 cealed them; the chlorophyll-bands are accumulated in the 

 middle of the joint-cell, and indeed broken up mto distmct 

 small cells containing starch and chlorophyll-vesicles. 



In the next joint-cell beneath, still almost unchanged, the two 

 colourless cells (vesicles) are seen to be scarcely more distended 

 than in the normal condition; the cell-nucleus lies between 

 them, surrounded by smaller hyaline colourless vesicles. The 

 chlorophyll-bands are unchanged. A similar phase is shown 

 in fig. 64, in Spyrogyra princeps [S. nitida, Kiitzing). 



In Spirogyra ? orthospira, the chlorophyll-bands are always 

 more delicate than in most other Spirogtjra, and are, under si- 

 milar conditions, more easily broken up into their component 

 parts. In the other species, one of these bands not unfrequently 

 continues entire, and, whilst more or less outstretched, swells 

 up in a saccular form, the keel-shaped thickened portion 

 spreads out, and the starch-corpuscles, that have heretofore 

 appeared only to adhere to the chlorophyll-bands, are then 

 seen to be contained within the interior of the cylindrical sac 

 so produced. 



These phenomena suggest the inference that the common 

 envelope of the chlorophyll-layer of S. orthospira is very thin- 

 walled and breaks down in water, whilst the enclosed vesicles 

 and cells possess a membrane that can resist the destructive ac- 

 tion of the water for a longer period, and byendosmosis undergo 

 great expansion ; that, on the other hand, in other species of 

 Spirogyra, in S. decimina, S. princeps, S. quinina, &c., the 

 secretion-cells are enclosed by a stronger and more resistant en- 

 velope united with the chlorophyll-sac. These bodies contained 

 within the chlorophyll- sac undergo, like a tissue-cell, the most 

 varied endogenous development : at first only chlorophyll- 

 vesicles, but at length thick-walled starch-corpuscles, of which 

 in many cases only the outer enlarged envelopes finally remain, 

 are aggregated together in the sacs like Conferva joint- cells. 

 This intimate study of the cycle of forms these chlorophyll-sacs 

 of the species of Spirogyra pass through is a necessary prelimi- 

 nary investigation towards a thorough apprehension of the mode 

 of development of joint-cells. 



The membrane of the secondary joint-cell is not apparent in 

 the example shown in fig. 72 ; it would seem to have swollen up 

 and to have melted away in the water at the cut end ; perhaps 

 it was in that stage of chemical metamorphosis which precedes 

 the thickening (lignification) . In the specimen represented in 

 fig. 70, it is seen contracted upon the enclosed cell-structures ; 

 the one small twin-cell still existing here is thus covered by 

 the chlorophyll-sacs, and hangs as by a thread to the septum of 



