444 HYPNACEiE. 



5. Amblystegium irriguum B. & S. (Hypnum irriguum 

 Hook. & Wils.) (Tab. LVI. C). 



Stems prostrate, with the divisions more or less pinnate, but 

 irregularly so, branches rather short, ascending or procumbent, 

 slender, forming intricate tufts of a deep olive green, the young 

 shoots brighter; stems tough, without paraphyllia, denuded at the 

 base. Leaves on the stems ovate, rather longly acuminate, the 

 point narrow and acute, but not slender and rather rigid ; at 

 base somewhat narrowed and slightly decurrent ; branch-leaves 

 narrower, ovate-lanceolate or oblong-lanceolate ; all rather solid 

 in texture and rigid, erecto-patent or more frequently somewhat 

 falcato-secund ; margin plane, sinuolate or obsoletely denticulate, 

 rarely if ever quite entire ; nerve very thick and wide, brownish, 

 becoming narrower and somewhat indistinct high up in the 

 acumen, but usually reaching to or nearly to the apex. Cells 

 hexagonal-rhomboid, obtuse or slightly pointed, 4-6 times as 

 long as broad, incrassate, rather opaque, somewhat narrower in 

 the acumen ; at base becoming gradually wider, irregularly 

 rectangular or quadrate, usually opaque, occupying the whole 

 base of the leaf and decurrent angles, not hyaline nor inflated, nor - 

 forming clearly-marked auricles. Seta rather long, firm ; capsule 

 strongly arcuate, sub-cylindric, contracted below the wide mouth 

 when empty. Autoicous. 



Hab. Stones in streams, principally on siliceous formations, rather rare. Fr. 

 summer. 



The stout nerve and solid, rather rigid leaves easily separate this and the two 

 following species from the allied plants ; A. varium is of much softer texture, with 

 thinner, more flaccid leaves, and narrower, though distinct nerve ; its leaves are more 

 usually entire, more ovate, with a more rapidly narrowing acumen, and the cells more 

 pellucid ; in the present plant the leaves are more ovate-oblong in outline, more 

 gradually tapering. A. fiuviatile differs in the still stouter nerve, especially at apex, 

 the less narrowly acuminate, often muticous leaves, and the entire margin ; and the 

 capsule is narrower and less arcuate. The differences between A. filicinum and the 

 present species are, in some forms of that plant, less marked ; as a rule it is a 

 less aquatic plant than the present species, more regularly pinnate, with the stem often 

 densely tomentose, and with numerous paraphyllia ; more or less aquatic forms, how- 

 ever, approach very closely to the present moss, and are sometimes difficult to 

 separate ; they prevail, however, in calcareous districts, where this species is rare ; the 

 branching is usually more regularly pinnate, and the leaves more cordate-triangular 

 and dilated at base, often more distinctly serrulate ; the most important characters are, 

 however, the presence of paraphyllia on A. filicinum, usually more or less numerous 

 both on stem and branches even in the more aquatic forms, and the basal angular cells, 

 which in that plant are always more or less hyaline and thin-walled, and clearly 

 marked off from the other basal cells. In the present plant the leaves are firmly 

 attached to the stem, and when detached often leave the decurrent angles remaining 

 adherent to the stem, but even when these are removed with the leaf they are hardly 

 distinct from the other basal cells, and are incrassate, comparatively small, and usually 

 dark and opaque, never hyaline and thin-walled. As regards the var. spinifolium 

 Schp., the student is referred to the note on A. filicinum. 



A. irriguum is not unfrequently submerged and floating, with elongated stems. 



