28 Prof. H. Karsten on the Formation, 
tum 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 into distinct 
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, Kiutzing). 
In Spirogyra? orthospira, the chlorophyll-bands are always 
more delicate than in most other Spirogyre, 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 sae 
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 by endosmosis undergo 
great expansion; that, on the other hand, in other species of 
Spirogyra, in S. decimina, S. princeps, S. quinina, &e., the 
secretion-cells are enclosed by a stronger and more resistant en- 
velope united with the chlorophyll-sac. These bodies contained 
within the chlorophyll-sae 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 bya thread to the septum of 
