— 2— 



perichaetial leaves is very instructive, as, if taken from the middle or 

 basal portion of the leaf, it shows toward either end the normal al- 

 ternation of large empty cells and small chlorophyll ones; after a 

 shorter or longer distance, according to the species and the proximity 

 of the section to the base of leaf, the chlorophyll cells become m^uch 

 enlarged, the others relatively smaller, until all are uniform. These 

 uniform cells have their corrmon walls pitted, they may contain as 

 Russcw noted, scattered chlorophyll grains, but appear otherwise 

 empty, at least in case of plants with m.ature capsules ; in fact a section 

 of the dry perichaetial leaves shows them almost entirely collapsed ; if 

 water be apolied to such a section under the microscope, the walls can 

 be seen to immediately sprirg apart (this test may also be applied to 

 leaves lying flat on the slide) and present then in hexagonal outline 

 with outer walls projecting angularly, an accordion effect, which on 

 sufficient soaking goes over, at least in part, to a series of nearly rect- 

 angular cells. The transverse contractibility of the perichaetial leaves 

 is greatly increased by this cellular structure, in which fact its physi- 

 ological function is .perhaps to be sought. 



The antheridial leaves of this subgenus present very little, if any, 

 difference from normal branch leaves, and antheridia are not easy to 

 find in herbarium material. Observations upon the organs of fructifi- 

 cation of Sphagnum^ preferably from the field and from fresh speci- 

 mens, are much needed ; so far as observed all species of this sub- 

 genus are always dioicous. 



The subgenus is cosmopolitan in its distribution; only to the 

 northward it probably does not extend quite as far as Litophloea : at 

 any rate it is not yet known from Greenland or Spitzoergen.^^^ 



1. Sphagnum portoricense Hampe, 1852. Warnstorf once expended 

 a whole article upon the proof that this species was not distinct from 

 5. imbricatum Hornsch.^~\ only to reverse his decision the year after, 

 his attention in the meantime having been called by Schliephacke to 

 the walls of the cortical cells of the branches.^^^ But this character had 

 already been mentioned in a number of works and very clearly figured 

 in no less than three.^*^ I allude to the fact because of its interest in 

 connection with the history of the species, also because it illustrates 

 two weaknesses of Warnstorf which we shall find frequently leading 

 him into error: 1. an insufficient consideration of the work of other 

 botanists, 2. unreliability in observations involving minute microscop- 



(1) Cf. C. Jensen, Musci Asiae borealis III. 5. 1909. 



(2) Hedwieia. 28: 303 -8. jp^. VIII and IX. 1889. 



(3) L. c. 29: 67,/. 1890. 



(4) Sullivant, Icon. Muse. ?), f.pl.2. 1864; Braithwaite, Month. Microsc. Jour. 

 14: 47, f., pi. ex. 1875. Sphagnaceae of Europe and North America, 32, 

 f.,pl.li. 1880. 



