ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 619 



cell-colonies of Hydrodictyon, and summarising the matter as follows: — 

 1. The cylindrical form of the cells and their union at their ends is de- 

 veloped by growth and pressure between the adjacent cells on the 

 principle of functional hypertrophy. 2. The large intercellular spaces 

 of the adult net have their origin in the shrinkage of the mass of the 

 mother- protoplasm during cleavage. 3. The central cavity of the net 

 is clue to the scattering of the swarm-spores under the influence of 

 chemical and food stimuli, and their coming to rest upon the mother- 

 cell- wall. 4. The form of the meshes is determined by the chance 

 grouping of the spores in coming to rest, their viscidity tending to 

 maintain chance contacts once established ; and the slight readjustments 

 due to gliding of their surfaces upon each other in the crowding in- 

 cident to their growth as spheres and when first beginning to elongate, 

 the number of sides of the polygonal meshes tending to become larger 

 the greater the amount of intercellular space which is present when the 

 spores come to rest. 



Urospora in Norway.* — 0. Hagem, when studying the algal Mora 

 of Drobak Sound in the spring of last year, found on some stones in 

 the littoral region several dark green patches containing three species 

 of Urospora — U. mirabilis, U. elongata, U. Wormskioldii ; the latter two 

 of which had previously been recorded only from the Arctic regions. He 

 describes and figures each of the three species, and discusses their struc- 

 ture, distribution, affinities, etc. 



Development of the Genus Ulva.f — J. Schiller has studied the de- 

 velopment of Ulva in the laboratory. He gives a detailed account of 

 the minute structure of the gametospores and their biology. He finds 

 that the process of conjugation is just as in Monostroma, Entermorpha, 

 and many Phreophyceas. He describes the germination and develop- 

 ment of the zygotes and of the gametes ; he describes the primary 

 and secondary rhizoids, the latter of which have a surprising power of 

 producing a new cell-filament, or rhizoid-shoot. Ulva and Ent&romorpha 

 are indistinguishable in their young stages, and there is a true branching 

 in both of them, arising from a similar division of the apical cell. In 

 both these genera three forms of gametes are found, macrogametes, 

 parthenogametes, and microgametes, and they occur four, eight, or 

 sixteen together respectively. 



Cell-wall Structure in Cladophora.J — P. Brand publishes some 

 notes upon the cell-membrane, transverse walls, and joints of Cladophora, 

 to supplement the information given by him seven years ago, in a 

 paper on the structure and growth of the plant. After a general con- 

 sideration of the structure of the membrane, he treats of the outer 

 lamella, the sheaths of the membrane, its constituent parts, its growth, 

 creases of the membrane, formation of transverse walls, formation of 

 joints. 



* Nyt. Mag. f. Naturvid. Christiana, xlv. (1908) pp. 261-9 (1 pi.). 



t SB. k. Akad. Wiss. Math. -Nat. Kl. Wien, cxvi. 1 (1907) pp. 1691-1716 (1 pl.\ 



I Ber. Deutsch. Bot. Gesell., xxvi. (1908) pp. 114-43 (lpl.). 



