ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 441 



wall, and must be formed by apposition and not by intussusception. This 

 was shown by the mode of deposition in the sheath of particles of salts of 

 iron and lead when the alga was grown in dilute solutions of these salts. 

 The passage of its substance through the cell-wall can be proved in a 

 similar way. 



The structure and origin of the gelatinous sheath in the Desmidieas is 

 essentially the same as in the Zygnemaceae; this is also the case with 

 Chsetophora and Sphwrozyga. 



In Chroococcus helveticus the gelatinous sheath is homogeneous and 

 capable of swelling, in Gloeocystis ampla it is composed of two successive 

 layers. The stalk of some diatoms (e. g. Gomphonema) is composed of a 

 gelatinous substance the density of which increases towards the outside ; it 

 swells but slightly, but is intensely coloured by anilin pigments. It is 

 entirely independent of the cell-wall. 



Among the Volvocineae the gelatinous sheath of Gloeomonas ovalis swells 

 greatly, that of Pandorina less, that of Gonium and Eudorina least of all. 

 The rod-structure is distinct in Pandorina and Gonium, less so in Eudorina, 

 while the sheath of Gloeomonas is apparently homogeneous. In Volvox the 

 separate individuals of a colony have no distinct sheath of their own, but 

 lie immersed in a common gelatinous mass which fills the interior of the 

 sphere. This gelatin is traversed by delicate strands of a denser and more 

 resisting material. Towards the periphery may be detected a membrane 

 of polygonal outline derived from the original walls of the separate cells. 



A gelatinous sheath can be detected in nearly all the Flagellata by the 

 use of sufficiently dilute staining materials ; and this sheath is evidently 

 due directly to the activity of the protoplasm. In Euglena sanguinea it is 

 secreted in the form of straight or more or less curved filamentous bodies. 

 In the social forms the gelatin consists of a fundamental substance, im- 

 mersed in which are denser granular corpuscles. Both substances are 

 coloured by anilin-pigments. The brown or black colour of the sheath of 

 these colonies is due to the deposition of oxide of iron. 



Anatomy and Development of Agarum Turner!.* — Mr. J. E. Humphrey 

 states that the anatomy of the Laminariaceai shows great uniformity ; 

 taking place, in this as in other species, by intercalary growth at the 

 junction of stipe and lamina. A pith, an internal cortex, an external 

 cortex, and an ej)idermis containing the coloured pigment, are here to be 

 distinguished. In young specimens the pith is not differentiated, the 

 differentiation only taking place slowly. M. Eeinke has described a 

 zone of growth as existing in the Laminariaceee ; this zone is present in 

 Agarum, but is accompanied by a second sub-epidermal cambium. As for 

 the perforations, the author shows how they are produced ; the blade is 

 covered with hollow conical papillae, the tissue diminishes at the apex of 

 the cones, then bursts, and the opening enlarges as the frond grows. 



Marine Vaucherias.t — Prof. 0. Nordstedt described the marine species 

 of Vaucheria of the English and Scotch coasts, the thickness of the fila- 

 ments, and length of the oogonia and antheridia, being accurately given. 

 V. sphserospora he describes as both monoecious and dioecious, and unites 

 with it V. suhsimplex. 



Binuclearia, a new genus of Confervace8e.| — Prof. V. B. Wittrock 

 describes under this name a fresh-water alga found at high altitudes in 



* Proc. Amer. Acad. Arts and Sci., 1886, p. 195 (2 pis.). 

 t Scottish Naturalist, 1886, 4 pp. and 1 pi. 



t Bot. Sallsk. Stockholm, Feb. 17, 1886. See Bot. Centralbl., xxix. (1887) pp. 60 

 and 89 (2 figs.). 



1887. 2 G 



