1897,] Vegetable Physiology. 231 
21° to 23° C. Optimum 30° to 35° C. for the European form, and 
30° to 87° C. for the Javan form. The maximum temperature for 
growth is 40° to 43° C. It cannot grow in juice kept at 43° C., but is 
not killed. The thermal death point of the frog spawn form is between 
87° and 88° C. (five minutes exposure), and of the nude form only a 
little lower, i. e., between 833° and 863° C. It is thought that possibly 
the thick sheath may have a protective use, as dried and stone-hard 
specimens brought from Java were found to be alive at the end of 3} 
years. A good contrast stain for the frog spawn form is dahlia fol- 
lowed by corallin—Erwrn F. SMITE. 
A New Disease of Tobacco Caused by Phytophthora 
nicotianz.—This disease, described by Dr. J. v. Breda de Haan,’ is 
tnost destructive to the seedlings while yet in the seed bed, but attacks 
older plants as well, extending its ravages under favorable conditions 
even to the curing barns. In this paper, published early in 1896, the 
author presents a very satisfactory account of the disease, and precedes 
the account by a general description of the location of the tobacco 
fields in the Dutch East Indies, The relations of soil and climate to 
the parasite are fully pointed out, as are the methods of culture both of 
the seedlings and of the mature plant. 
The disease is, so far as he has been able to determine, confined to 
the Dutch East Indies. It has probably caused some damage for many 
years, but was first generally recognized in 1889. In 1893 it was very 
destructive, owing to the wetness of the season. 
The hyphz of P. nicotianz enter the leaf by the stomata, and ramify 
principally in the intercellular spaces. They also pass through the 
cells, and sometimes fill them with a net-work of hyphe. 
Usually only the haustoria enter the cells. The haustoria are simple 
unbranched hyphæ, which end freely in the cell. 
The mycelium is normally unicellular; but when it is torn, or when 
the protoplasm is contracted, on account of unfavorable external con- 
ditions, the cell contents are separated from the empty part of the 
mycelium by thin cross walls. ; 
The contents are granular, with scarcely any oil drops, and stain 
readily with an aniline blue. The hyphæ are about 5 mic. mill. thick, 
and when free to do so grow long and scarcely branched. Sometimes 
they may be seen reaching from one seedling to another, looking like 
delicate threads. 
! (De. Bibitziekte in de Deli-Tabak veroorzacht door Phytophthora nicotiane, 
Mededeelingen uit's Lands Plantentuin, Number XV, 1896.) 
