172 THE .TornxAL OF noTAxr 



turquoise-green colour, and the pale gonidia then stand out very 

 clearly in contrast with the normal green, their contents becoming 

 sharply outlined. It is interesting to note that pale cells are met 

 with in freely growing Chlorococcum. They appear to a very large 

 extent to be invaded by fungoid hyphaj in some specimens. There is 

 every indication that these pale cells of the Chlorococcum are identical 

 with the " pale cells " of lichens, but, as far as I know, nothing has 

 been said about them in the literature of the subject. It is evident 

 that when Prof. Elf ving examined these " pale gonidia," he inferred 

 that gonidia were formed by the transformation of the extremities of 

 hyphal cells into spherical masses. 



Regarding the connection between the hyphse and the gonidia in 

 the substance of the lichen, the following facts must be noted. Thin 

 microscopical sections make it possible to observe with certainty that 

 all the gonidia have not a close connection with the hyphse. Some, 

 generally a small number, are either not in contact at all with the 

 hyphae, as is particularly the case in the more or less strongly deve- 

 loped groups of gonidia ; or the contact is so superficial that pressure 

 on thin sections, by means of the cover glass, causes a certain number 

 of the gonidia to become separate from the thallus : so that, even 

 with the most careful observation, it is absolutely impossible to detect 

 any adherent particles of hyphse or of anything else. Such gonidia, 

 in the great majority of cases, appear to be well-developed spherical 

 cells with a regular cup-shaped chloroplast. The fixed sections of 

 such gonidia, from which chlorophyll has been withdrawn, take a 

 rather deeper tint on staining. But the correct interpretation may 

 be that most gonidia are more or less closely connected with the 

 hyphse, varying from a simple contact to actual fusion with them. 



Most often the gonidia are found in a network of hyphae, as the 

 figures in every textbook of botany will show. The surrounding 

 hyphae are stimulated to bud and many fine hyphal threads cover the 

 gonidia all over, and in this way hold the algal cells in a hyphal 

 envelope. This fact, in my opinion, speaks for itself. 



The conditions appear to be quite natural ; the hyphae being 

 brought into contact with the gonidia acquire an abnornaal generative 

 power which shows itself in an abundant budding and in the forma- 

 tion of short processes, generally filled with protoplasm, spread over 

 the surface of the gonidial cells and extending from one algal cell to 

 all the others in the neighbourhood. In this way whole groups of 

 gonidia are commonly observed which are woven and tied into a single 

 mass by short branches of the hyphae. These offshoots of the hyphaj, 

 first described circumstantially by Bornet, were named extracellular 

 haustoria by Schwendener. 



The al)0ve general description of the connection between hyphae 

 and gonidia must be supplemented by a more detailed examination of 

 one particular example. Elfving made the following observation, 

 which he misinterpreted. From the parts of the hyplue spread over 

 the gonidial layer, and also from the other hyphal masses, pear-shaj^ed 

 swellings extrude, which adliei-e so closely to the gonidia that they 

 appear one with them. Such swellings generally leave the hyphal 

 branches as lateral offshoots, but sometimes the hyphie terminate as 



