474 BOTANICAL GAZETTE [DECEMBER 
ness on the inner walls, so far as these differences are due to the convexity of 
the inner walls, may become less and less until they fall below the liminal value 
as a stimulus.’”—C. R. B. 
Symbiosis in orchids.—A recent paper by BERNARD?’ recalls his previous 
studies on the germination of certain orchid seeds and on the relation of fungi 
to the tuberization of orchids and potatoes. The present paper advances our 
knowledge of these fungi and places considerable emphasis upon their place in 
the development of the orchid group. Three species (Rhizoctonia repens, R. lanu- 
ginosa, and R. mucoroides) have been recognized, described, isolated, and grown 
in pure cultures for considerable periods. though no spore-bearing structures 
have been observed, they probably belong to the lower basidiomycetes. The 
first-named species seems to be the most primitive and most widespread in its 
symbiosis. 
Two series of orchids were studied, those of epiphytic and those of terrestrial 
habit. The growth of th dling plished experimentally in test tubes 
upon suitable media, and the effect of the fungi and of various concentrations 
of the media upon their development carefully studied. The results are most 
interesting and suggestive, and may be summarized as follows: (1) Orchids 
exhibit a progressive development of symbiosis corresponding to and probably in 
some measure the cause of their development in phylogenetic series. (2) The 
evolution in epiphytic and terrestrial families is parallel, and symbiosis is the 
only common factor which can account for this parallelism. (3) The evolution 
in symbiosis manifests itself in an advance from independent germination of see 
with normally developed seedlings, to a germination entirely dependent upon the 
infection of the embryo by fungi and the development of seedlings characterized 
by protocorms. In the adult plants various progressive stages of symbiosis 
are exhibited, from an intermittent infection with sympodial habit to permanent 
symbiosis associated with the monopodial habit of the host. (4) The fungi vary 
in virulence according to their species, their host, and the length of time ‘they 
have lived outside those hosts. Very virulent cultures act upon more highly 
developed orchids in a similar manner to more attenuated cultures upon more 
primitive species. (5) Concentrated solutions of the culture media have an 
effect upon germination similar to that produced by infection by fungi, and both 
symbiosis and growth in concentrated media result in increasing the concentra- 
tion of the cell contents, which seems to be the necessary condition for the develop- 
ment of these specialized plants.—Gro, D. FULLER. 
Recent contributions from the Gray Herbarium.?°—A. EasTwooD pat? 
Am. Acad. 44:563-591. 1909) has published a ‘Synopsis of the Mexican an 
28 BERNARD, Noét, L’évolution dans la symbiose. Les orchidées et leurs cham- 
pignous commensaux. Ann. Sci. Nat. Bot. IX. g9:1~196. 1909. ; 
20 Contributions from the Gray Herbarium of Harvard University, New Series, 
No. XXXVI (Proc. Am. Acad. 44:563-637. 1909); and No. XXXVII (Proc. Bost. 
Soc. Nat. Hist. 34: 163-312. pls. 23-30. 1909). 
