256 SUMBIARY OF CURRENT RESEARCHES RELATING TO 



ovary of au apetalous pistillate flower, aud looks like a small plump 

 dust-pan. The body of the " pan," which is horizontal inclining to 

 cernuous in position, is formed of two broad oblong scales, subconcave 

 at base, and j)laced close side by side. Here then, we have a stipe, six 

 bracts, five scales, and a germ, in all thirteen separate elements, com- 

 pletely differentiated, regularly combined, and adapted to each other in 

 the most systematic fashion. 



Apospory in Pteris aquilina.* — Prof. W. G. Farlow describes an 

 instance of apospory in the common brake. On pinnae which presented 

 a peculiar curled apj)earance, some of the sporanges had developed at an 

 early period into abnormal structures, while others were altogether 

 replaced by such. Some of these abnormal structures presented most 

 resemblance to the protoneme of a moss, others to the prothallus of a 

 fern. On none of them had antherids and archegones been formed. 



Xerotropism in Ferns, j — By the term xeroiropism Prof. A. Borzi 

 designates the tendency of plants, or of parts of plants, to alter their 

 position in order to protect themselves from desiccation. The property 

 is but rarely exhibited among Phanerogams, much more frequently 

 among Cryptogams, J especially in the vascular section. Among Thallo- 

 phytes, however, we find it displayed by many Oscillariacese, and by 

 species of Ulothrix aud Schizogonium. Among Vascular Cryptogams, 

 striking examples are afforded by many species of Selaginella, and by 

 ferns growing in dry or stony situations, such as Aspleniam Trichomanes, 

 and several species of Ceteracli and Notochlsena. The structure adapting 

 the fern to this end is especially described in the case of Ceterach 

 officinarmn. 



Under prolonged desiccation the leaves of this fern become com- 

 pletely rigid, the lamina recurving itself on the upper surface, and 

 exposing the under surface covered with brown scales. A few hours of 

 rain are sufficient to cause the leaves to resume their normal position 

 and appearance. The xerotropic movement is more vigorous in young 

 than in adult leaves ; each pinna has a movement independent of that 

 of the others. 



The anatomical structure which gives rise to these movements is as 

 follows. The upper epiderm is composed of large cells with wavy 

 sinuous walls somewhat thickened and collenchymatous. When dry they 

 contract considerably in the transverse direction, and this is accomi^anied 

 by a corresponding enlargement of the subjacent tissue, the lower 

 mesophyll having very thin cell-walls, and being abundantly supplied 

 with intercellular passages. The palisade-parenchyma takes no active 

 part in the movements, but its cells are affected by the contraction of 

 the epiderm, and their chlorophyll-grains are transferred from their 

 radial walls to the lower portion of their cell-cavity. 



Similar structures are described in Notoclilaena vellea, Asplenium 

 Trichomanes, aud several species of Cheilanthes. 



Structure of the Commissure of the Leaf-sheath of Equisetum.§ 

 — Dr. C. Miiller enters in great detail into the mathematical questions 

 connected with the arrangement of the sheath-teeth of Equisetum and of 



* Ann. of Bot., ii. (1S88) pp. 383-5 (4 figs.\ Cf. this Jouinal, 1S87, p. 996. 



t Nuov. Giorn. Bot. Ital., xx. (18S8) pp. 477-82. 



X Cf. this Journal, 1888 p. 1001. 



§ Jahib. f, Wi£s. Bot,— (Prin-sheira) xix. (1888) pp. 497-579 (£ pis. and 5 figs). 



