BOG XEROPHYTES AND ACID SOILS. 121 



Otis (1914 : 478) has determined the transpiration-rate of several 

 reed-swamp dominants and subdominants, namely, Pontederia cor- 

 data, Typha latifolia, Sagittaria latifolia, Scirpus validus, and Scirpus 

 americanus, in comparison with that of the water-Hly, Castalia odo- 

 rata and a free water-surface. The highest rate was shown by Scir- 

 pus and the lowest by Sagittaria. The maximum for one day in 

 cubic centimeters per square decimeter was as follows: Sagittaria, 

 1.05; Pontederia, 1.812; Typha, 2.129; Castalia, 2.28; free water, 

 2.281; Scirpus americanus, 3.198; S. validus, 3.690. It is significant 

 of the relation of the transpiring surface to the incident rays that 

 the water-lily and free water gave the maximum on the same day, 

 the two rushes on another day, and the three species with erect or 

 ascending leaves on still another day. 



Dosdall (1919 : 29) has made a comprehensive study of the water- 

 relations of Equisetum, dealing with its transpiration, growth, echard, 

 etc. It was found that Equisetuin fluviatile wilted at a water-content 

 of 25 per cent. Ranunculus sceleratus at 13 per cent, Helianthus annuus 

 at 5.6 per cent, and Equisetum hiemale at 5 per cent. Experiments 

 with both plants in the same pot showed that Equisetum fluviatile 

 wilted in from 2 to 7 days in contrast to 10 to 12 days for Helianthus, 

 and 2 to 12 days in contrast to 17 to 19 for Phaseolus. Equisetum 

 arvense wilted in 5 days, while Helianthus required 12 days. The 

 transpiration-rate of Equisetum fluviatile was 25 per cent greater 

 than that of the hydrophytic Ranunculus sceleratus, about twice as 

 great as that of Helianthus, thrice higher than that of Phaseolus, and 

 10 times as great as in the xerophytic Bryophyllum calycinum. The 

 water-loss of E. hiemale was slightly greater than that of Helianthus 

 and much greater than in Phaseolus, while in E. arvense it about 

 equaled that of the latter. All three species of Equisetum guttated 

 vigorously in the greenhouse at night, as well as when placed under 

 bell-jars, showing that the roots have marked powers of absorption. 

 The growth of Equisetum fluviatile was much better in mud or when 

 submerged than in a water-content of 35 per cent, branches failing 

 to develop well in the latter, and its water-loss was also much higher 

 in mud. The stomata of both E. fluviatile and E. hiemale were found 

 to be constantly open, as in hydrophytes generally, and they were 

 more than three times as numerous in the more hydrophytic E. 

 fluviatile. The author concludes that the latter is a true hydrophyte, 

 its xerophily being only superficial and probably due to the persis- 

 tence of ancestral characters, while Equisetum hiemale and arvense 

 are more mesophytic in their tendencies. 



The comparative water-relations of conifers are hardly sufficiently 

 known as yet to make their behavior in bogs entirely clear, but it 

 seems probable that species of Picea, Abies, and Pinus readily 

 withstand the low soil-temperatures found there in consequence of a 



