NUTRITIVE ORGANS OF CELLULAR PLANTS. S23 



The homogeneity of their nature has been remarked 

 by all who have studied them, and the names of Frons 

 and Thallus have been given to the mass of which they 

 are composed : it is only by abbreviation that sometimes, 

 in the descriptions of Fuci, stems, leaves, or roots, are 

 spoken of, to designate portions of the thallus which 

 have these different appearances. 



Proofs of this homogeneity are often found on observ- 

 ing their manner of living : all parts of the thallus of 

 Algffi appear almost equally endowed with nutritive 

 faculties ; they all absorb the water which is in con- 

 tact with them, exhale oxygen, but appear to live in an 

 almost independent manner, and only transmit the juices 

 to the rest of the tissue with difficulty, or perhaps not 

 at all. Thus, when a Fucus or Ulva is found only half 

 sunk in water, the submerged part is fresh, but the other 

 withers and dries up, — a remarkable phenomenon, wliich 

 may result either from the plant not transmitting juices 

 from one part to the other, or from the evaporation being 

 too active in the portion exposed to the air for the others 

 to supply it. 



The thallus presents very distinct degrees of texture, 

 which have served Lamouroux and Fries as the basis 

 of their classification ; some, as the Fucaceae, are 

 coriaceous, and of an olive colour ; others, as the 

 Floridess, are cartilaginous, and more or less rose- 

 coloured. There are some entirely membranous, as 

 the Ulvaceae ; and gelatinous or semi-gelatinous, as the 

 Batrachospermese. 



The Algae are almost all of them,* at least in their 

 infancy, fixed upon the solid parts which form the 

 bottom and edges of waters. Sometimes they are 



* According to Vaucher, Zygnema and Hydrodyction are free in their 

 infancy. 



