PROTOPHYTIC AND OTHER FUNGI. 329 



colored spheres, of nearly equal size, each of which had its own cellulose 

 wall; and it can scarcely be doubted that on the escape of these from the 

 parent cyst, each would lead an independent life resembling that of its 

 progenitor. It seems probable, moreover, that the outlying masses of 

 the protoplasmic extension may detach themselves and live independ- 

 ently, each forming a cellulose envelope for itself. But until 'conjuga- 

 tion ' or some other kind of sexual union shall have been discovered in 

 this curious organism, we cannot be said to know its whole life-history; 

 and the peculiar interest which attaches to it renders the further study of 

 it in the highest degree desirable. It may be hoped that the excellent 

 observer by whom it has been brought to our knowledge, may ere long 

 find himself able to supply the missing link. 



325. LICHEES. The Microscopic study of this group has latterly ac- 

 quired a new interest for the Botanist, from the remarkable discovery 

 announced in its complete form by Schwendener in 1869 1 (and now ac- 

 cepted by the highest authorities) that instead of constituting a special 

 type of Thallophytes, parallel to Alga (with which they correspond in 

 their vegetative characters) and Fungi (to which they are more allied in 

 fructification), they are really to be regarded as composite structure, hav- 

 ing an Algal base, on which Ascomycetous Fungi ( 318) have sown 

 themselves and live parasitically. As, however, they do not furnish ob- 

 jects of interest to the ordinary Microscopist (the peculiar density of their 

 structure rendering a minute examination of it more than ordinarily 

 difficult), nothing more than a general account of their curious organiza- 

 tion will here be attempted. The Algal 'thallus' of a Lichen belongs to 

 the group of PalmellacecB ( 243) or its allies; and consists of cells termed 

 gonidia usually green, but sometimes red or bluish-green interspersed 

 among long cellular filaments. The proportion between these two com- 

 ponents of the thallus varies in different examples of the type. Thus, in 

 the simplest Wall-lichens, the Palmella-like ' primordial cell' gives 

 origin, by the ordinary process of cell-division, to a single layer of cells, 

 which spreads itself over the stony surface in a more or less circular 

 form; and the ' thallus,' which increases in thickness by the formation of 

 new layers upon its free surface, has no very defined limit, and, in con- 

 sequence of the slight adhesion of its components, is said to be ( pulveru- 

 lent.' But, in the more complex forms of Lichens, the thallus is mainly 

 composed of long fibre-cells, which dip down into the superficial layers 

 of the bark of the trees on which they grow, and form by their inter- 

 weaving a hard crustaceous ' thallus ' in which the gonidia are imbedded, 

 sometimes irregularly, sometimes in definite layers, covered by an 

 envelope of interlacing filaments. It is from this Algal portion of the 

 structure, that the soredia of Lichens are formed; which are little projec- 

 tions of the surface, composed of single or aggregate gonidia, invested by 

 fibre-cells, and falling, when dry, into a powder, of which every particle 

 is a bud, capable of reproducing the plant from which it proceeded. 



326. Ths fructification of Lichens, on the other hand, is really the 

 production of their Fungal overgrowths, which are nourished by the Al- 

 gal vegetation. The Lichen-forming Fungi, in fact, live upon their 

 Algal hosts, like the Entophytic Fungi (such as the 'blights' of corn, 

 219) which infests the higher forms of Vegetation ; each of the former 



1 See his memorable work " Ueber die Algentypen der Flechtengonidien " 

 (Basel, 1869), which is said by Prof. Sachs ("Text-book of Botany," p. 273) to 

 have settled for the future the place of Lichens among the Ascomycetes, and Sir 

 J. D. Hooker's Presidential Address to the Royal Society, 1878. 



