NOTES AND ABSTEACTS. 



383 



The author concludes that the real limiting factor to the growth 

 of other than special peat-plants is not evaporation or temperature 

 but the poisonous nature of the substratum. The toxins produce a 

 physiological drought, which in the case of wheat decreases the 

 absorption of the roots by about 50 to 65 per cent. 



An intimate and controlling relation exists between soil bacteria 

 and the plants growing in the central zone. — G. F. S. E. 



Peat-bOg"S in Michigan. By George Plumer Burns {Bot. Gaz. 

 pp. 105-125, Aug. 1911; 8 figs.).— This is No. 8 of the author's 

 botanical survey of the Huron Eiver Valley, and is entitled '* Edaphic 

 Conditions in Peat-bogs of Southern Michigan." The author and 

 others find the following characteristic zones : (1) Submerged plants 

 to 12 feet or more in depth, Chara, Ceratophyllum, Naias, and Pota- 

 mogeton'^; (2) Water Lily, shallow w^ter, seldom over 5 feet; (3) Float- 

 ing Sedges, the mat formed is very firm and is usually 18 inches thick 

 {Gar ex filiformis, Menyanthes, Drosera,, Equisetum limosum, Scutel- 

 laria galericula-ta, &c.); (4) Bog Shrubs, Chamaedaphne, Andromeda 

 'polifolia, Betula pumila, Vaccinium Oxycoccos, Sarracenia, &c. ; 



(5) Tamarack, Larix laricea, Osmunda- regalis, Rhus vernix, &c. ; 



(6) Poplar and Maple, Acer ruhrum, Populus trevmloides, Quercus 

 rubra, Solanmn Dulcamara, Geum rivale, Solidago, .&c. ; (7) Marginal, 

 Willows, Salix nigra, Ruhus spp., Alisma Planiago-aquatica, Lycopus, 

 Polygonum Hydropiper, Ranunculus sceleraAus (?), &c. 



The temperature of the air in these bogs (at the level of the leaves) 

 is much colder during the night and early morning than that of the 

 surrounding upland, for cold air drains into these basins, which, are 

 low-lying, often with steep banks. But in the day-time the tem- 

 peratures may be very high. This is illustrated by several tables of 

 observations. The temperature of the soil shows, however, very slow 

 variations during the season (except that of the uppermost layer). 

 Thus, e.g., in the last week of July the soil at 18 inches deep was 

 only 6° 0. in the Tamarack and 7.5^ C. (Bog Shrub and Poplar zones), 

 IQo 0. Bogsedge. 



On the other hand, at 1 inch in depth, the rise of temperature 

 in the soil is quite rapid, and resembles that of the surrounding 

 uplands. The variation in air temperature was sometimes as much as 

 25.5° 0., whilst that of the soil was only about 1° 0. 



The level of water in the soil shows extraordinary differences 

 according to the season, and even in the same season in different plant 

 zones. 



In Mud Lake, in consequence of a series of alternately wet and 

 dry years, a section of the moss showed alternating layers of 

 Sphagnum and Polytrichum. 



As showing the different water-levels in different parts of the 

 peat-moss, the water-table was 18.4 inches below the surface in the 



* A few- of the British species in each formation are quoted here. 



0 c 2 



