288 BOTANICAL GAZETTE [Marcu 
activities as generally as or with anything like the rigidity assumed by some 
workers. e fact of vicarious conditions, or stimuli, renders the conception 
of limiting factors less definite. In some light requiring seeds, for instance, 
several things can be substituted for light, as salts, higher temperatures, acids, 
To speak of the lack of sufficient light as a limiting factor to germination 
helps little. What should be learned is, what internal condition, or inhibitor, 
may any one of these factors act upon to initiate growth? The conception 
of an external condition as a limiting factor frequently leads physiologists to 
fail to examine the internal mechanism upon which that and other factors play 
to bring about a given result. The reviewer feels that the law of the minimum 
should be applied to biological problems with due realization of its limitations. 
—Wws. CROCKER. 
Vegetation of Pennsylvania.—A description of the vegetation of the 
western part of Pennsylvania, by Cripss,% is organized upon a physiographic 
basis, including the swamp, lake-forest, ravine-valley, river, and upland series. 
The plant succession in each series is outlined and the composition of the prin- 
cipal associations indicated. The upland forest serves to indicate the interest- 
ing position of the flora, partaking of the northern forms, as seen in Pinus 
Strobus, Betula lutea, and B. lenta, combined with such typically southern 
species as Magnolia acuminata. The dominant members of the climax forest 
are found to be Fagus grandifolia, Castanea dentata, Quercus alba, and Acer 
rubrum. With these are associated such others as Tsuga canadensis, M. agnolia 
acuminata, Liriodendron Tulipifera, and Tilia americana.—GEo. D. FULLER. 
Germination of spores.—BRIERLY?’ has done an interesting piece of work 
upon spore germination which he summarizes as follows: ‘The ripe ascospores 
of Onygina equina will germinate directly after a prolonged resting period, which 
may be curtailed or eliminated by a preliminary treatment of the spores with 
artificial gastric juice, but not by subjection to low temperatures. The fu ull 
grown unripe ascospores and the chlamydospores will germinate immediately 
in the absence of digestive treatment.”’ Demand for a rest period is common 
in seeds. Frequently the need for a rest period is imposed by the presence of 
seed coats. Likewise BrrieR.y believes this need is imposed in this form by 
the presence of the spore coat.—Wm. CRocKER. 
Crisss, J. E., Plant associations of western Pennsylvania with special reference 
to pbyblogtanikc sélationship. Plant World 20:97-120, 142-157. 1917. 
7 Brierty, WiILtiAM B., Spore germination in Onygina equina Willd. Ann. 
Botany 31:127-132. 1917. 
