1922] CURRENT LITERATURE 335 
and its capacity for exposure to the air. Gart has made some exact studies to 
determine the controlling factors in distribution.” High light requirement 
is well shown by the fact that the average vertical distance occupied by Fucus 
on south slopes is over 2 m., while on north slopes it is less than one-third of a 
meter. North exposures with a high shore line have no Fucus at all, and there 
water surface. Well grown Fucus plants receiving less than one-fourth total 
light become darker in color, and decomposition takes place. From these 
considerations it is properly concluded that light is a ‘erterelling factor in 
determining the lower limit of Fucus.—H. C. Co 
Vegetation of the Dry Tortugas.—The Tortugas are the westernmost of 
the Florida keys, and are the seat of a marine laboratory of the Carnegie 
ho se 
speaking broadly belongs entirely to the strand nen Even Rhizophora is 
tions. Four communities are cad. dominated ear by Uniola 
paniculata, Suriana maritima, Opuntia Dillenii, and Chamaesyce buxifolia. A 
detailed account then follows of the special vegetation of each of the eight 
keys that make up the group. Of especial interest is the author’s comparison 
of the vegetation of the islands in rors and 1916 with their vegetation in 1904, 
as reported by Lansinc.—H. C. Cow es. 
ophulariaceae and Orobanchaceae.—BorsHoRE™ has reached the 
conclusion that the Orobanchaceae represent an extreme offshoot from the 
of ees details, the author concludes that there is ample evidence “to show 
that direct and distinct continuity can be established from non-parasitic 
througn semi-parasitic Scrophulariaceae to the most degraded parasites of the 
family, and that these again show direct continuity with the still more degraded 
* Gam, FLoyp W., Some experiments with Fucus to determine the factors con- 
trolling its vertical distribublon:, Publ. Puget Sound Biol. Sta. 2:139-151., 1918. 
, H. H. M., Botanical ecology of the Dry Tortugas. Carnegie Inst. 
Washington Publ. 252:109-138. pls. 6. figs. 7. 1918. 
™ BorsHorE, I., The morphological continuity of Scrophulariaceae and Oro- 
banchaceae. pone Bot. Lab. Univ. Penn. 5:139-177. pls. 12-16. 1920. 
