ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 473 



of the pericarp. The various modes may be arranged under four 

 different types, viz. : — 



1. In the genera of Campanulaceae, Campanula, Adenophm-a, Tra- 

 chelium, Phyteuma, and Specularia, the pores are formed between the 

 veins of the pericarp, and are due to the bending outwards of wedge- 

 shaped masses of sclerenchyma in particular parts of the dissepi- 

 ments. 



2. In the genus Masschia the opening of the pericarp is the result 

 of several superposed transverse fissures, in consequence of a rupture 

 of the thin portions of the pericarp- wall between the masses of vascular 

 bundles. 



3. In AntirrMnum and Linaria the pores arise in previously formed 

 projections at the apex of the capsule, and the bursting takes place 

 suddenly and irregularly. 



4. In Papaver the pores are the result of the contraction and 

 bending upwards of the rays of the stigma ; a loculicidal pore being 

 formed corresponding to each partial loculus of the capsule. 



Dorsiventral Structure of the Roots of Orchidese.* — M. E. de 

 Janczewski has examined the structure of the aerial roots of a number 

 of OrchideaB, and finds that, while many have a radiar structure like 

 that of the earth-roots, others, as those of Aeranihus fasciola, Phalae- 

 nopsis amahilis, Sarcanthus rostratus, and Epidendron nocturnum, have 

 a remarkable dorsiventral structure which is much the most strongly 

 developed in the first-named. 



In the aerial roots of this epiphytic orchid — which are of great 

 length compared to the very abbreviated leafless stem, and are the 

 only assimilating organs — the velamen consists, on the upper surface 

 and the margin, of only a single layer, which perishes very early, 

 giving a dark-green colour to these parts; while the under side, 

 where the velamen is well developed, is white. The root-hairs and 

 air-chambers are confined to the under side ; the latter are in connec- 

 tion with the intercellular system. The central vascular cylinder has 

 the ordinary radiar structure. 



Externally these roots are flat on the upper side, with deep longi- 

 tudinal furrows, the under side forming a projecting angle ; and the 

 history of development shows that this structure is congenital and is 

 not the result of external conditions, such as light. 



Roots acting as Leavesf — Dr. Fritz Miiller reports a unique 

 instance of an epiphytic orchid, Aeranthus, which, though only con- 

 sisting of roots and heads of small flowers, nourishes itself indepen- 

 dently, since the long, much coiled roots contain chlorophyll, and thus 

 act as leaves. 



Vernation and Methods of Development of Foliage as protective 

 against Radiation.^ — Eev. G. Henslow describes the vernation and 

 mode of opening of the leaves of a number of woody and herbaceous 



* CR. Acad. Sci. Cracovie, xii. (1884). See Ann. Sci. Nat. (Bot.), ii. (1885) 

 pp. 50-81 (3 pis.). 



t Kosmos, ii. (1885) p. 443. See Biol. Centralbl., v. (18S6) p. 765. 

 X Joum. Linn. Soc. Lond. (Bot.), xxi. (1S80) pp. 624-33 (15 figs.). 

 Ser. 2.— Vol. VI. 2 I 



