ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 623 



the combining procarpial cells. This complex nucleus then undergoes 

 repeated division, and the daughter-nuclei pass, one through each of the 

 diverticula, into the placental cells, there to fuse with their nuclei, this 

 union being followed by division. This process occurs throughout the 

 whole placenta, so that in the end each of the placental cells from which 

 the spores are directly formed, has received into its nucleus part of the 

 substance of the nucleus formed by the fusion of the nucleus of the 

 " spermatium " with that of the carpogenous cell. 



The procarpial cells of Gracilaria are homologous with the auxiliary 

 cells in Dudresnaya ; but, owing to the concentration of these cells 

 round the procarp, there is no need of the long connecting-tubes of the 

 latter genus, which are replaced by the protoplasmic protrusions or 

 diverticula. Nothing was seen corresponding to the production, in 

 Dudresnaya, of several cystocarps from a single procarp. 



Frond of Champia parvula.* — Mr. E. P. Bigelow confirms the 

 observations of Debrayf on the structure of the frond of this seaweed, 

 and adds also particulars regarding those of C. salicornioides, Lomentaria 

 Baileyana, and L. Coulteri. 



Development of Hydrurns.J — Herr G. Lagerheim finds this alga 

 extraordinarily abundant in the neighbourhood of Freiburg-i.-B. in the 

 winter and spring, disappearing in the summer, as it grows only in cold 

 running water. Each individual is inclosed in a slimy gelatinous 

 envelope which differs in consistency at different parts of the thallus, 

 but is quite structureless. The cells are dispersed through this jelly ; 

 towards the apex of the branches they are in close contact with one 

 another ^ but in the older parts of the thallus they are at some distance 

 apart ; while at the base, above the point of attachment, they are again 

 crowded. In each cell are one or two parietal chromatophores, coloured 

 brown by phycopheein, accompanied apparently by phycoxanthin. Each 

 chromatophore contains a lenticular pyrenoid, and probably a single 

 nucleus. In the lowest part of the protoplasm are several small vacuoles, 

 some of which can be distinctly seen to pulsate. Each cell is surrounded 

 by a very delicate membrane, possibly of the same substance as the 

 envelope, but containing less water. 



It is only the cells of the branches which produce zoospores, each 

 cell in this position giving birth to either two or four. They force 

 their way through the deliquescent cell-membrane and envelope, and, 

 when mature, are of very peculiar form. When mature they are tetra- 

 hedral, each angle being prolonged into a slender colourless beak; in 

 one of the angles is a brown chromatophore ; and in the centre of the 

 side opposite to the chromatophore a single short cilium, and near it two 

 pulsating vacuoles, but no pigment-spot. The zoospore moves very 

 slowly with its cilium in front. After a time it rounds itself off. They 

 appear to germinate directly without conjugation. 



Hydrurus probably remains in a dormant state through the summer 

 and autumn. The author has found at this time on stones in streams 

 collections of roundish cells inclosed in jelly, which may be the palmella- 

 condition of the alga. He has observed the formation of resting-spores, 

 which are produced, like the zoospores, in the branches, about 15 //, in 



* Proc. Amer. Acad. Arts and Sci., xxiii. pp. 111-20. See Eot. Centralbl., 

 xxxiv. (1888) p. 99. t See this Jom-na], 1887, p. 624. 



X Ber. Dcutsch. Bot. Gesell., vi. (1888) pp. 73-85 (5 tigs.). 



