188 Prof. H. Karsten on the Formation, 
Very commonly, indeed, an intimate reciprocal relation does 
appear to exist between the cuticle and the neighbouring cells ; 
but this can scarcely ever be regarded as a production of the - 
former from the latter. 
Although the want of a cuticle upon the epidermic tissue of 
the roots, while it occurs upon stems of the same age, might seem 
to give support to such an explanation, still the cork-formation 
occurring in the latter immediately after an injury to the cuticle, 
or the cuticular layers replacing it, may be regarded as giving 
probability to a directly opposite supposition. And indeed the 
cuticle is really present at an earlier period than the epidermis. 
The peculiar development of the membranes of Gidogonium 
also affords an equally remarkable and interesting proof of the 
mutual dependence of neighbouring cells. For the horizontal 
rupture of the integument in a circular form over the adjacent 
fold of the joint-cell is not to be explained merely by the fact that 
the extraordinary thickening of the membrane of the joint-cell 
assimilates to itself all nutritive material, and therefore excretes 
nothing for the integument. The latter must then always re- 
main thinner at this spot than in other parts,—which, however, 
is not the case. On the contrary, the cuticle appears to be quite 
uniform throughout up to the period of the rupture; its rup- 
ture is preceded by a disintegration of its substance, almost 
appearing as if it were decomposed into a deliquescent mucila- 
ginous and an insoluble granular part, as may be seen especially 
in the cases described on page 284, vol. xii. (PI. V. fig. 25), in 
which no extension of the joint-cell has taken place. 
The conditions observed in Spirogyra even lead rather to the 
supposition that the products of the metamorphosis of the cuticle 
may serve as nourishment for the adjacent membrane of the 
joint-cell. 
It is true that the Spzrogyre, and probably all the Conjugate, 
possess no true cuticle, but the primary membranes of the mother 
cell fulfil the function of this integument ; and the phenomena 
presented by these may therefore probably be interpreted as 
analogous to those of cuticular development. 
If Spirogyra orthospira be allowed to vegetate for some time 
in distilled water, the very thick cuticular layer is gradually 
reduced until at last it almost completely disappears, a very thin 
innermost lamina excepted. In carbonic-acid water this pheno- 
menon takes place still more rapidly, but simultaneously the 
primary membranes of the joint-cell increase in thickness. On 
the contrary, if organic compounds be added to the water, the 
cuticular layer is very perceptibly thickened; the joint-cells 
cohere more firmly together, and are not separable with the 
same facility as in the former case. 
