CORNISH SPHAGNA 265 



pore-development has been a response to aerial conditions of growth, 

 such submerged forms may perhaps be viewed as having reverted to 

 the aquatic habit without losing the characteristic pore-development. 

 This in turn suggests a possible explanation of the pseudopores of 

 aS'. crassicladioii as reversions from the aurlculatum type. 



At any rate, there does seem some reason for regarding the firm- 

 ground Suhseciinda ?i^ organised for rapid transpiration. Growing as 

 they do in soil which, though firm, is still saturated, the scarcity is 

 not of water, but, as pointed out by Mr. J. A. Wheldon {Collect ion, 

 Taxonomy, and Ecoloffy of the Sphagna, 191S), of mineral food. 

 Spreading long-pointed leaves, with pores most numerous on the most 

 exposed portions, must be conducive to the quick passage of soil- water 

 through the plant, and the incurving of the leaf-margins, usually a 

 check on transpiration, must have an exactly opposite effect when the 

 pores are doi-sal instead of ventral. Apparently, too, the amount of 

 exposure determines the number of pores. Mr. E. C. Horrell 

 {European Bpliagnacece, p. 63) states, "In the examination of plants 

 belonging to this section it is important that both the branch- and 

 stem-leaves should be selected from the upper part of the stem, just 

 below the capitulum " — implying that the pore-development is thei'e 

 most typical. 1 find, too, that where the branches just below the 

 capitulum are prolonged at the apices into attenuate points the more 

 or less imbricate basal leaves of these branches will be porose only in 

 the upper (exjDOsed) half or three-fourths, while the narrow full}-- 

 exposed leaves of the attenuate points wdll be porose throughout their 

 length. 



It is interesting to notice that the dorsal pore-arrangement here 

 suggested as enabling these plants to occupj^ situations too diy for 

 most Sphagna are reproduced in the only other species which seem able 

 to survive similar conditions, viz. S. plumiilosum and its near allies. 

 The two groups have other points of resemblance. In the field the 

 eye learns to distinguish tufts of the Siohsecunda from those of 

 aS'. plunmlosum by the j^ellowish colour of the former and the more or 

 less falcate arrangement of the capitulum branches, but where these 

 characters are lacking tufts of the Subsecicnda may easily be passed 

 over as belonging to the Aciitifolia. Generalizations are perhaps 

 unsafe, but observations in the field, under the perhaps peculiar 

 conditions of the West Cornwall moors, would suggest that whereas 

 drier conditions destroy the Cuspidata and in the Cymhifolia induce 

 a dense stunted growth, the Acutifolia and Suhsecunda have evolved 

 taller, lax, and sometimes rather plumose forms with an adequate 

 transpiration device which have much more successfully overcome 

 the difficulties of the drier situation. 



Most of the plants mentioned in the following list have been 

 seen, and many of them named, by Mr. W. R. Sherrin or Mr. J. A. 

 Wheldon, or both. The nomenclature and arrangement are those of 

 Mr. Wheldon's Synopsis of the European Sphagna, 1917. Localities 

 in East Cornw^all are indicated by (2) ; the remainder are in West 

 Cornwall. 



Sphagnum fmhriatum Wils. var. validius Card, and var. inter- 

 medium Russ. Bog near Cheesewring (2) ; from the same locality 

 Mr. Sherrin collected var. rohustum Braith. and var. laxi^olium AV. 

 Journal of Botany. — Vol. 60. [September, 1922.] t 



