ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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not observed in any species of Ebinanthaceae, Droseracese, Cruciferae, 
Papaveracete, or Cyperaceae ; aquatic and arenaceous plants are destitute 
of it ; it is found only in those which grow in humus. In Drosera the 
author observed a peculiar condition of the roots; the long brown 
root-hairs are invested by a dense mantle of dead vegetable remains, 
Sphagmm-leiiYeSy &c., only the tips of the roots remaining exposed. 
New American Phytophthora.* — Mr. E. Thaxter describes a new 
Pliytoplithora, P. PJiaseoli, parasitic on the pods, stems, and leaves of 
the Lima bean, Phaseoliis lunatus. The mycelial hyphae are branched, 
rarely penetrating the cells of the host by irregular haustoria ; conidio- 
phores slightly swollen at their point of exit through the stomates, 
arising singly or one to several in a cluster, simple or once dicho- 
tomously branched, and with one or more inflations below their apices ; 
conids oval or elliptical, with truncate base and papillate apex, 35-50 /x 
by 20-24 jx. Germination by zoospores, usually fifteen in number, or 
rarely by a simple germinating hypha. Oosperms unknown. 
Beer-yeasts.’i' — M. E. C. Hansen shows that all the species of SaccJiaro- 
myces pass, in their evolution, successively through the different forms 
which Eeess regarded as specific. The latter based his species on 
characters drawn from the form of the cells. The author’s results were 
obtained by means of cultivations started from a single cell. 
This method, conceived in 1882, has enabled the author to establish 
that the high and low ferments are not convertible the one into the other, 
and the opposite results obtained by Pasteur and Eeess must have been 
due to a mixture of the two species. 
According to the author, the species of Saccharomycetes are defined 
by the temperature curves of the development of their spores, by critical 
temperatures (death, &c.), by the budding, and by the fermentative power. 
If various kinds of Saccharomyces be cultivated under identical 
conditions, the form of the individual cell furnishes specific charac- 
teristics for the whole group and accordingly for the species, although the 
course of spore development remains the most important characteristic. 
Yet the form of the single cell should only be employed for recognition 
purposes with the greatest caution, because almost all kinds of the genus 
Saccharomyces may appear under the same form, although of course not 
under the same conditions. It would, therefore, seem easy to transform 
one species into another if the favourable conditions were ascertainable ; 
but Prof. E. C. Hansen, after more than four years’ experimentation, 
has failed with the aid of variations of temperatui’e to transform the low 
yeast into the high yeast, and vice versa. 
In practice it was of course important that the cultivation should be 
quite pure, and this was effected by starting from a single cell ; yet in 
the case of the low yeast Carlsberg 1, very different appearances were 
obtained : some of the cells might have been taken for S. pastorianus^ 
others for those of S. cerevisise. In cultivations in beer- wort S. cerevisise 
did not alter in form, while S. pastorianus, which at first retained its 
sausage-like shape, completely lost it after several generations. So that 
the difference between the two series of experiments became constantly 
less and less, and finally in both oval cells only appeared. That the 
* Bot. Gazette, xiv. (1889) pp. 273-1. t Aun. dc Microgr., i. (1888) pp. 11-18. 
