48 SCIENCE PROGRESS 



consists of three zones surrounding a central area "of short 

 grass (Boutelona gracilis, Bulbilis dacty hides). Next the 

 central area is a zone exhibiting more vigorous growth and 

 different floristic composition, next follows a bare zone of 

 dead vegetation where usually only a few annuals are present. 

 Still further out is a second narrow stimulated zone, where 

 the fruit bodies of the fungus are produced. When the myce- 

 lium first begins its development, it spreads out equally in 

 all directions ; the stimulation in the outermost zone is attri- 

 buted to the utilisation of the organic material available by 

 the fungus and consequent increase in nitrogen content. The 

 next phase represented by the bare zone is brought about by 

 the great increase in mycelial development and consequent 

 decrease in soil moisture, so that only ephemeral species flourish 

 if rains are frequent. The third phase represented by the 

 broad inner zone of stimulated vegetation marks the period of 

 decay of the mycelial complex with accompanying liberation of 

 nitrogenous material ; this phase is associated with an invasion 

 of ruderal species which give place to short-lived grasses, and 

 finally to the grasses of the natural turf which occupy the 

 centre. The annuals of the bare zone comprise such species 

 as Plantago purshii, Festuca octoflora, Hedeoma hispida, and 

 Lepidium ramosissimum. These species luxuriate in the inner 

 stimulated zone, and in addition the following are character- 

 istic : Chenopodium incanum, Lappula occidentale, Cryptanthe 

 crassisepala, and Amaranthus blitoides. The third zone com- 

 prises Schedonnardus panniculatus sometimes accompanied by 

 Malvastrum coccineum and Sitanion hystrix. 



Morphology. — In the January number of the Annals of 

 Botany, Prof. Bower makes a further contribution to the 

 study of the Phylogeny of the Filicales dealing with the Ptero- 

 idea?. 



P. A. Murphy describes the sexual organs of Phytophthora 

 erythroseptica. The oogonial rudiment grows through the 

 antheridium and on emerging at the other side forms an 

 oogonium. Each sexual organ primarily contains numerous 

 nuclei, but about two-thirds of these degenerate whilst the 

 remainder undergo a single division. The oogonium exhibits 

 differentiation into ooplasm and periplasm and, as a consequence 

 of the degeneration of all the nuclei in the latter and one of 

 the two daughter nuclei of the former, a uninucleate oosphere 



