Recently Treboux[239] has revised the work done by Artari and Beyerinck in reference to _Cystococcus humicola_. He denies that two physiological races are represented in this alga, the lichen gonidia, in regard to the nitrogen that they absorb, behaving exactly as do the free-living forms of the species. He finds that the gonidium is not a peptone-carbohydrate organism in the sense that it requires nitrogen in the form of peptones, inorganic ammonia salts being a more acceptable food supply. Treboux concludes that his results favour the view that the gonidia are in an unfavourable situation for receiving the kind of nitrogenous compound most advantageous to them, that they are therefore in a sense “victims” of parasitism, though he qualifies the condition as being a lichen-parasitism or helotism. This view does not accord with Chodat’s[240] results: in his cultures of gonidia he observed that with glycocoll or peptone, which are nearly equivalent, they developed four times better than with potassium nitrate as their nitrogenous food, and he concluded that they assimilated nitrogen better from bodies allied to peptides. _c._ EFFECT OF SYMBIOSIS ON THE ALGA. Treboux’s observations however convinced him that the alga leads but a meagre existence within the thallus. Cell-division—the expression of active vitality—was, he held, of rare occurrence in the slowly growing lichen-plant, and zoospore formation in entire abeyance. He contrasts this sluggish increase[241] with the rapid multiplication of the free-living algal cells which cover whole tree-trunks with their descendants in a comparatively short time. These latter cells, he finds, are indeed rather smaller, being generally the products of recent division, but mixed with them are numbers of larger resting cells, comparable in size with the lichen gonidia. He states further, that the gonidia are less brightly green and, as he judges, less healthy, though in soredial formation or in the open they at once regain both colour and power of division. Treboux had entirely failed to observe the sporulation which is so abundant at certain seasons.