300 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



entirely absent. Whether P. infestans forms oospores normally in 

 diseased Potato stems is an important question which awaits further 

 research ; but now that the oospores have been definitely examined 

 and studied, it is possible to speak more certainly as to the identity 

 of those resting spores that several writers have found in dead Potato 

 haulm. — A. D. C. 



Pinks, Double, To Recognize. By J. Lavalle (Rev. Hort. de I'Alg., 

 No. 10, p. 336, Oct. 1912). — It is asserted by a practical gardener, 

 M. Jacoulet, of Lux, that it is possible to distinguish double from single- 

 flowered seedlings of Pinks at a very early stage of their growth. All 

 double-flowering seedlings have three cotyledons ; single-flowering 

 ones have only two. This is said to be proved by four years' 

 observations. — M. L. H. 



Plant Food in Relation to Feeding. By Cyril G. Hopkins 

 (U.S.A. Exp. Sin., Illinois, 1912). — A paper showing that better results 

 can be obtained by the use of suitable fertilizers in rotation than can be 

 obtained by crop rotations alone without fertilizers. — G. P. C. 



Plasmopara viticola, Spore Germination and Infection with. By 



C. I. Gregory {Phytopathology, ii. pp. 235-249; Dec. 1912 ; figs.). — 

 An account of the mode of germination of the oospores of Plasmopara 

 viticola is given with figures. In all cases observed a germ tube was 

 produced which bore at its apex a single conidium. The germination 

 of this conidium has not been followed, but the author believes it to 

 follow the lines of the ordinary conidia and to set free from 1 to 17 

 swarm spores, but usually from five to eight. After swimming about 

 for some time they become quiescent, and later germinate by sending out 

 germ tubes which infects the vine leaf through the stomal openings. 



F. J. C. 



Pneumathodes in Begonia. By V. Vouk (Ber. d. deutsch. hot. 

 Ges. xxx. 257-262 ; 1912 ; 1 plate). — On the stems of various marsh 

 plants, and on the roots of some epiphytic orchids, curious structures 

 termed pneumathodes have been described by various writers. These 

 organs are special aerating tissue masses having the same functions 

 as stomata and lenticels, and serving to replace or to supplement 

 these more usual types of organ for the passage of gases into and out 

 of the plant. Vouk now describes a peculiar type of pneumathode 

 found in several species of Begonia, but especially well developed on 

 the stem of shrubby species like B. vitifolia, B. aptera, B. undulaia, 

 and some others which have perennial aerial stems. At first sight 

 these organs resemble lenticels, but they are green, and there is no 

 cork-cambium layer underlying them as in the case of lenticels, which 

 in these species are apparently replaced by this special type of aerating 

 organ. Each pneumathode is covered by a small-celled epidermis, 

 the cells having very thin walls and no distinct cuticle, hence allowing 

 the ready passage of gases ; below the epidermis the green tissue 



