TRANSACTIONS OF SECTION K. 787 



the Anabcuna spaces of Azolla leaves, and the Nostoc cavities in Anthoceros thallus 

 shows a similar association of the alga with nitrogen-fixing bacteria in these 

 plants. In thin microtome preparations fixed with Bonin's fixative, and stained 

 with Kiskalt'e amyl grain-stain both Azotobacter and Pseudomonas can be readily 

 identified among the algal threads. A mixed culture of the two organisms can be 

 obtained by crushing some Azolla leaves or Anthoceros thallus on a slide in dis- 

 tilled water under sterile conditions, inoculating a solution consisting of water, 

 100 c.c. ; mannite, 1 grm. ; maltcose, 1 grm. ; potassium phosphate, 0'5 grm. ; and 

 magnesium sulphate, 0'02 grm. ; and incubating at 24° C. for two days. Micro- 

 scopical examination with Kiskalt's amyl grain-stain and Ziel's carbol fuchsin 

 shows the culture to be a mixture of Pseudomonas and Azotobacter. 



Agar plates made by adding 1 grm. of agar-agar to the above nutrient solution, 

 and inoculated with a few drops of crushed Azolla leaves or Anthoceros thallus, 

 gave in two days the typical round colonies of Azotobacter and ovoid colonies of 

 Pseudomonas. It is possible that this association is advantageous to the host 

 plant — the alga supplying the necessary carbohydrate for the nitrogen-fixing bac- 

 teria, and the host plant absorbing some of the nitrogenous product. 



2. Notes on the Distribution of Halophytes on the Severn Shore. 

 By J. H. Priestley, B.Sc, F.L.S. 



These notes are the result of a detailed study of a small area on the left 

 bank of the Severn between Lyttelton Worth in Gloucestershire and Burnham 

 in Somerset. They refer more especially to the pelophilous formations in 

 this area. Analyses have been made of the salt content and water content of the 

 soils from representative spots within the area, and as a result it has been possible 

 to draw certain conclusions as to the connection between drainage and plant zona- 

 tion. The plant distribution within the zones showed certain anomalies, but these 

 can probably be explained by reference to the soil analyses. 



The general adaptation of the plants of the pelophilous zone to their habitat 

 is discussed, and it is suggested that this formation is disappearing somewhat 

 rapidly from most parts of this coast. 



3. Plant Distribution in the Woods of North-East Kent. 

 By Malcolm Wilson, B.Sc. 



In this district a large proportion of the woods is coppice with standards, 

 felling taking place about every fourteen years. There is little variation in the 

 altitude, and the plant distribution depends chiefly on the character of the soil. 



The following can be distinguished : — 



1. Beech type on the shallow soils of the chalk. The standards are chiefly 

 beech, the undershrubs consisting of yew, oak, hazel, Cornus sanguineus, Euony- 

 mus europceus, and Ligustrum vulgare. Viola hirta, Verbascum Thapsus, 

 Euphorbia amygdaloidcs, and Mercurialis perennis are abundant. 



2. Ash-hazel type on the ' clay with flints ' on the chalk. Hornbeam is fre- 

 quently found; oak standards are usually present. Mercurialis perennis is 

 abundant, with Primula vulgaris and Scilla nutans. 



3. Chestnut type on the Thanet sand ; usually coppice with chestnut or oak 

 standards. Rubus fruticosus is often present. On the deeper deposits Scilla 

 nutans is abundant, with Lychnis diurna and Adoxa Moschatellina. Aspcrula 

 odorata and Solidago Virgaurea are characteristic of this formation, 



4. Oak-birch-heather type on the Woolwich and Keading series and on the 

 Oldhaven pebble beds. Pinus sylvestris is frequently found here. The woods are 

 usually thin and open; heather and bracken are abundant, with Luzula pilom and 

 Rumex Acetosella. The soil is usually strongly acid. 



5. Oak type on the London clay ; usually coppice with oak standards. Bracken 

 is abundant, and many plants found in woods of the preceding type occur. There 

 is usually a sharp distinction between the woods occurring on the calcareous soils 

 and those on the tertiary formations. In the former the'soil acidity is slight or 

 none, and Mercurialis perennis is abundant; in the latter the soil is acid and 



