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 (Edogonium 

 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. xiii. (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 Spirogyrce, and probably all the Conjugatse, 

 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 firnaly together, and are not separable with the 

 same facility as in the former case. 



