436 Prof. Meyen's Report of the Progress of 



has succeeded in doing this will in part be shown in the course 

 of this report from the observations of other botanists. 



Mohl finds this homogeneous substance most clearly in the 

 Algae between the cells, which are combined by it into a 

 whole. 



In the Nostochinete, Rivularice, in Protococcus, Palmella, 

 HydruruS) Oscillatorza, Scytonema, &c. the more or less thick 

 mucous or gelatinous substance is to be regarded as the 

 analogue of the intercellular substance in the perfect plants. 

 In the proper Confervae the common mucous substance has 

 disappeared, or only forms a very thin envelope over the 

 fibres, so that these are lubricated and rendered slippery by 

 it, but no longer combine into masses; instead of which they 

 possess a homogeneous external tube. Of the true Con- 

 fervas the Spirogyrce of Link are those which possess the 

 greatest mucous envelope, and in those, as also in other Con- 

 fervae, we can observe that this mucous substance becomes 

 thicker with increasing age, and that in the young plants it 

 is entirely wanting. According to this, the view which Mohl 

 has advanced on the nature of intercellular substance can 

 hardly be extended to this substance. 



In the more compound Algae this mucous matter, accord- 

 ing to Mohl's observation, is not only disposed on the surface 

 of the entire plant, but also between the individual cells, which 

 had already been observed by Eysenhard and Agardh ; and 

 since this homogeneous substance entirely fills the intervening 

 space of the cells, the intercellular passages are totally want- 

 ing in these vegetables. In the thallus of Ferns the intercellular 

 substance forms a less remarkable constituent part than in the 

 Algae. In this case it is the cells of the outer layer becoming 

 transparent in water, which are connected by this substance, 

 so that here also no intercellular passages remain. In the 

 more perfect plants it is not so easy to demonstrate the pre- 

 sence of intercellular substance, as in these not only do 

 the cells lie in closer contact with each other, but since also 

 intercellular passages run between their parenchymatous cells. 

 Mohl however alleges that notwithstanding these difficulties, 

 we may still succeed in many cases in meeting with this mass 

 interfused between the cells, in greater or smaller quantities, 

 even in perfect plants, so that there will be scarcely any plant in 

 which we shall not be able plainly to demonstrate this sub- 

 stance in one organ or other. Mohl then enumerates a num- 

 ber of instances in which the intercellular substance is found 

 in mosses, ferns, in the wood of the Coniferae and of the Di- 

 cotyledones. The intercellular substance shows itself more 

 plainly in the protended thick-sided cells which often occur 



