204 DR. COHN, ON THE DEVELOPMENT OF 



requisite for the maintenance of their organism, from the 

 elements carbon, oxygen, hydrogen, and nitrogen, and some 

 oxides and salts, which are afforded to them in the surround- 

 ing medium, in the form of carbonic acid, ammonia, and 

 water ; they do not, therefore, require any organic nutriment, 

 but are enabled to vegetate in pure water ; they can decompose 

 the water or the carbonic acid, and evolve oxygen in the 

 sunlight, acquiring at the same time a green or red colour, 

 from the development of chlorophyll or some analogous 

 colouring matter. The Fungi, on the other hand, like 

 animals and most parasitic plants, have not the power of 

 spontaneously producing, from inorganic nutriment, the 

 materials requisite for the maintenance of their vital pro- 

 cesses — these must be afforded to them in the form of already 

 organized compounds ; they cannot, therefore, flourish where 

 this nutriment is not afforded to them, either in a living or in 

 a dead and decaying organism, or at any rate in water in 

 which a considerable amount of organic matter is not dissolved, 

 as in an infusion ; they evolve no oxygen, and do not become 

 green in the light. Partly, from the latter circumstance, 

 Nageli distinguishes the Fungi from the Algae by the want of 

 chlorophyll, or some analogous colouring matter. But that 

 the presence or absence of chlorophyll affords no sufficient 

 character to distinguish the one class from the other, is suffi- 

 ciently obvious, when we consider the variableness exhibited 

 in this respect, in several classes of plants, especially in those 

 of parasitic habits, many of which, it is true, are colourless, 

 but others, such as the Santalaceae, Rhinanthacese, and Loran- 

 thaceae, have chloi'ophyll in abundance ; whilst others again, 

 not of parasitic nature, or not known to be so, as many of the 

 Orchids, are colourless. The presence also, of chlorophyll in 

 many of the ' Protozoa,' as Hydra viridis, Bursaria viridis, 

 &c., is sufficient to indicate the uncertainty of any character 

 thence derived. The circumstance of the plants growing in 

 water, or in the air, has been employed to distinguish the 

 Algae from the Fungi — it being stated that the former inhabit 

 water, and that the latter flourish only in the air ; but that 

 this distinction is untenable is at once obvious, when it is 

 remembered that it often happens that of species even in the 

 same genus, as Vaucheria, Ulothrix, JProtococcus, Sec, some 

 vegetate in water and others in the air. 



The difficulties which attend the separation of the lower 

 Alffo^ and Fungi have led several authors, as Kiitzing, to 

 propose, for some of them, the erection of a group termed 

 Mycophgcecp, under which he includes those Thallopli-ytes 

 which agree with the rest of the Fungi in their vital con- 



