216 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of which tliey float on the water — an arrangement similar to that 

 found in the white and yellow water-lilies. 



Swelling of the Pea.* — F. Schiudler has investigated the phe- 

 nomena of the swelling of the seeds of Papilionaceae in the case of ten 

 varieties of Pisum sativum. He finds all the three stages indicated by 

 Nobbe well displayed in all cases ; but each variety was characterized 

 by special peculiarities. The power of swelling was found in general 

 to be in proportion to the specific gravity of the seed. The following 

 may be stated as the general results of the investigation : — 



The first penetration of water into the testa of the pea usually 

 takes place through the microjjyle, which, with few exceptions, 

 provides an open communication with the external air. Advantage is 

 next taken of the longitudinal fissure of the hilum. The anatomical 

 structure of the layer of stellate parenchyma presents great facilities 

 for swelling ; and this absorbs a large proportion of the water admitted 

 through the micropyle, the quantity being sufficient for the first 

 development of the embryo. The spiral vessels of. the testa serve as 

 ca2)illary tubes for the conduction of water. 



Aril of Ravenala.j — According to Dr. F. R. v. H5hnel, the aril 

 of the seeds of the " traveller's tree," Ravenala madagascariensis, is, 

 ■when fresh, of a beautiful azure-blue colour, and is the only known 

 example of an aril from which an oil is obtained for economical 

 purposes. J The author believes that in this instance the bright colour 

 prevents the seed being eaten by birds. The aril is entirely cellular 

 in its structure, the cells being elongated, thin-walled, and with very 

 small intercellular spaces. They are filled with a homogeneous, 

 finely granular, blue mass, consisting of protoplasm and an oil which 

 contains the blue pigment in solution. This substance appears to be 

 peculiar to the species, and of unknown composition. 



Structure and Mechanics of Stomata.§— S. Schwendener describes 

 in detail the points of anatomical structure connected with the 

 opening and closing of stomata. 



Of the contrivances on which the motility of the guard-cells 

 dejiends, the most important is that which the author describes as the 

 " epidermal hinge " (Haiitgeleiih), which is placed right and left of 

 the guard-cells in the outer wall of the adjoining epidermal cells. It 

 consists of a thin spot in this wall, never wanting in plants with a 

 thick-walled epidermis, though frequently absent from those where it 

 would be superfluous, viz. where the outer wall of the epidermis is 

 thin. In those cases where the stomata are depressed, they are sur- 

 rounded by delicate lamellfe of cellulose, which constitute the hinge, 

 attached either to the margins of the fissure, or to the round opening 

 which perforates the outer wall of the epidermis. 



The wall which separates the guard-cell from the adjoining 



* Wollny's Forscli. aus Geb. der Agriculturphysik, iv. (1881) p. 190. See 

 Bot. Centralbl., vii. (1881) p. 360. 



t Oestorr. Hot. Zeitschr., xxxi. (1881) pp. 386-7. 



X The aril of tlie tuitraeg (raace) yields a well-known oil. — Ed. 



§ MB. K. Akacl. Wiss. Berlin, 1881, pp. 837-67 (1 pi.). 



