844 SUMMABY OF CURRENT RESEARCHES RELATING TO 



lary tissue beneath the fructification, scattered groups of gonidia 

 wliicli are larger and of lighter colour than the normal gonidia of the 

 thallus, and which might easily be mistaken for cephalodia. They 

 are, in fact, derived from the normal gonidial layer, and, under favour- 

 able conditions, become gradually transformed into the scales in 

 question. They should strictly be regarded as a part of the fructi- 

 fication. In Peltidea aphthosa the apothecia have a different origin 

 from that in the nearly related genus Peltigera, viz. from immediately 

 beneath the gonidial layer. The endogenous origin of this peculiar 

 thallus-formation can be proved by following it out from the first 

 isolation of the gonidia to their complete differentiation into cortical, 

 gonidial, and medullary layers. No similar formation was observed 

 in Peltidea venosa. 



Fungi. 



Thermotropism of the Roots of ^thalium septicum.* — Dr. J. 

 Wortmann has further investigated this phenomenon, first observed 

 by Stahl, and finds the optimum temperature for its manifestation to 

 lie between 35° and 40' C. With exposure to unequal temperature 

 above 36°, he finds the plasmodia to be negatively, while below this 

 limit they are positively thermotropic ; both kinds being thus capable 

 of being induced on the same plasmodium. This phenomenon he com- 

 pares to that of Phycomyces, the fructification of which is negatively, 

 while the mycelium is positively geotropic. The thermotropic pheno- 

 mena of Plasmodia are closely analogous to those of roots. 



Plasmodiophora Alni.'j' — Dr. H. Moller has further investigated 

 the peculiar swellings caused by this parasitic fungus {ScMnzia Alni 

 Wor.) on the roots of the alder, which he finds on almost every 

 specimen examined of both Alnus glutinosa and incana. The proto- 

 plasm of the parasite is imbedded in a sac of the protoplasm of the 

 host, and this protoplasmic envelope is connected by several strings 

 with the parietal protoplasm. The protoplasm of the host remains 

 comparatively unaffected ; and hence the small amount of damage 

 done by the parasite. Both in this and other points, the physiological 

 processes present a great resemblance to those of Plasmodiophora 

 Brassicse. 



Nutrition of Trees by "means of Underground Fungi.J — Herr 

 B. Frank has made the remarkable discovery that the roots of 

 certain trees are unable to derive nutriment directly from the soil, 

 but do this entirely by means of a mass of fungus-hyphae which 

 entirely invests the root, and to which he gives the name MycorJiiza. 

 If the absorbing organs of our native oaks, beeches, hornbeams, chest- 

 nuts, or hazels are examined, they are found to consist of a nucleus, 

 the true root, and a cortex organically associated with it in growth, 

 composed entirely of fungus-hyphse, completely enveloping the whole 



* Ber. Deutsch. Bot. Gesell., iii. (1885) pp. 117-20. 

 t Ibid., pp. 102-5 (4 figs.). See also pp. 177-8. 

 J Ibid., pp. 128-45 (1 pi.). 



