TRANSACTIONS OF SECTION D. 745 



The grasses comprise the following 2G species : — 



Phalaris arundinacea, L. *Briza media, L. 



* Antho.vanthum odoratuni, L. Poa annua, L. 



Alopecurus geniculatus, L. *Poa pratenns, L. 



* Alopecurus pj-atensis, L. *Poa trivialis, L. 



PMeum jtratense, L. Glyceria aquatica, Sm. 



Agrostis alba, L. Glyceria Jliiitans, Br., et Tar 



*Agrostis vulgaris. With. Festuca duriuscula, L. 



Aira ccespitosa, L. Festuca elatior, L. 



*£[olcus lanatus, L. *Festuca pi-atensis, Huds. 



*AuenaJlavescens, L. Festuca loliacea, Huds. 



* Arrhenatherum anenaceum, Beauv. Bronius racejnosus, L. 



Phragmites communis, Triii. *Bromus mollis, L. 



* Cynosurus aistatus, L. *Lolium perenne, L. 



Another list is given, numbering twenty-five species, of grasses growing in the 

 same locality, but never appearing upon the water-meadows. The cause of their 

 absence is discussed ; the behaviour of two of them, Catabj-osa aquatica, Beauv., 

 and Dactylis glomerata, L., is found difficult to explain. 



The Gramine<e of the waterrmeadows are next contrasted with those occurring 

 upon very old non-irrigated grass land in Rothamsted Park, Hertfordshire (' Phil. 

 Trans.,' Part IV., 1882), where twenty species have been recorded. Thirteen 

 species, present both on the water-meadows and in Rothamsted Park, are distin- 

 guished by means of asterisks in the above list. Three Rothamsted species, ^I'ewa 

 pubescens, Huds., Dactylis glomerata, and Festuca ovina, L., are not found upon the 

 water-meadows. Seven water-meadow species do not occur at Rothamsted, viz., 

 Phalaris arundinacea, Alopecurus geniculatus, Agrostis alba, Phragmites communis, 

 Glyceria Jluitans, G, aquatica, and Bromiis racetnosus. 



The struggle for existence amongst the water-meadow grasses is discussed, and 

 various morphological and physiological peculiarities of different species are noticed, 

 particularly in their relation to this struggle. The local distribution of certain 

 species, even within the limits of the meadows, is also mentioned. 



Three species, Lolium perenne, Festuca pi-atensis, and Glycera Jluitans, exhibit 

 numerous variations, which are described. 



The hay crop is probably of far more constant botanical composition than that 

 of ordinary meadows, whereon it differs markedly (' Phil. Trans.,' Part I., 1880) 

 with the character of the season. On the water-meadows the effect of seasonal 

 variations in rainfall is largely eliminated, so that temperature and the duration 

 of .sunlight become the dominating factors. Assuming that, in accordance with the 

 researches of Boussingault, Gilbert, Risler, and Herve-Mangon, it requires a cer- 

 tain total amount of heat above an ascertainable minimum temperature to ripen 

 the seed of any given plant, this amount will be the earlier acquired the hotter the 

 season, and certain species will benefit to the extent that more of their seed will 

 fall to the ground, and so they gain an advantage in the struggle. 



Agriculturally Bromus and Holcus are the most objectionable of the water- 

 meadow grasses. The former, being annual, might be reduced in quantity by 

 early mowing year after year ; this, however, might only serve to stimulate the 

 vegetative growth of the latter. 



11. Juncus Alpinus, Vill., as new to Britain. By Chaeles Bailey. 



The author reported to the Section the discovery of this plant at Blair Athole, 

 in Perthshire, by Dr. F. Buchanan White, of Perth, who had sent an example for 

 exhibition to the Section. 



12. Studies on some New Micro-organisms obtained from Air. By Mrs. 



Peecy Fkankland and Peect F. Feankland, Ph.D., B.Sc. {Lond.), 



F.O.S., F.I.C., Assoc. Roijal School of Mines. 



In some papers on the micro-organisms present in air, previously communicated 

 to the Royal Society by one of us, the relative abundance of microbes in the air of 



