ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 73 



tion of light does not provoke formation of zoospores in plants grown 

 in nutritive solution : while on the other hand they are produced 

 both by diminution of light and by transference into diluted nutritive 

 solution. (Fj. pluviale also produces zoospores when it has been cultivated 

 in cane-sugar solution and this is replaced by diluted Knop's solution. 



Resting cysts of H. pluvialis which have lived in old foul water in 

 bright light, develop swarm-spores when transferred to distilled water, 

 or when provided with suitable nitrates (nitrate, nitrite, ammonium 

 salts). Light is not necessary to produce this result, though it enhances 

 the effect considerably. Cysts of H. pluvialis, which have been for a 

 long time in darkness, form swarm-spores when they are again lighted 

 or when they receive cane- or grape-sugar. 



Algal Vegetation of Ponds.* — N. Walker has examined certain 

 ponds situated above the Bramhope railway tunnel, near Leeds, occupy- 

 ing excavations in clay which were made sixty-seven years ago. He 

 mentions three available sites for algre, and gives the species found on 

 each. Site 1 : Winter shoots of CEnanthe fistulosa which form a pale 

 green zone, from 2-3 yards wide, extending from the edge of the pond 

 to a depth of about 9 in. Several factors which probably control the 

 succession of algal associations are mentioned, and the species occurring 

 in the various months are enumerated. Site 2 : Shoots of Potamogeton 

 natans and Sparganium ramosum occurring in the deeper water (1—3 ft.). 

 The vertical distribution of the alga? on these shoots is in some cases 

 striking, and seems to be affected by surface commotion caused by wind 

 and by differences in the illumination. Species of CEdogonium and 

 Bulbochcete are followed by Spirpgyra Weberi and other filamentous algae, 

 to be displaced in their turn by species of Mougeotia and Desmids. 

 Site 3 : Short decaying shoots of the smaller flowering plants, which 

 cover the floor of the pond in shallower parts not occupied by CEnanthe. 

 The dominant alga is Glceocystis vesiculosa. In one shallow pond with 

 deep mud, Spirogyra longata dominates throughout the year. The 

 movement of Phormidium inundatum along the filaments of Spirogyra 

 from the bottom to the surface is described. 



New Green Algae. f — F. S. Collins describes five new species, some 

 of which have already been distributed in the Phycotheca Boreali- 

 Americana. They are only in part from New England localities, but so 

 general is the distribution of plants of this class that the author states 

 they may be found in any temperate locality. The species in question 

 are : Pleurococcus marinus, Chcetomorpha chelonum, Cladophora amphibia. 

 Vaucheria longipes, and V. Gardneri. The two species of Vaucheria are 

 figured. 



Copulation and Germination of Spirogyra.} — A. Trondle is the 

 most recent investigator of Spirogyra. Other writers have left doubtful 

 certain details in the behaviour of the nuclei with regard to sexual pro- 

 cesses, and the present author is able to add fresh facts on these points. 

 He describes phenomena which vary from those generally known, 



* Rep. Brit. Assoc. York, 1906, pp. 758-9. 



t Rhodora, ix. (1907) pp. 197-202 (1 pi.). 



X Bot. Zeit., lxv. (1907) pp. 187-217 (1 pi., 13 figs, in text). 



