THUIDIUM. 381 



100. THUIDIUM B. & S. 



Primary stem prostrate, irregularly divided ; secondary 

 stems regularly pinnate, bipinnate or tripinnate . Paraphyllia 

 numerous, multiform. Leaves dimorphous, the stem-leaves 

 differing much from the branch-leaves, single-nerved, strongly 

 papillose. Capsule rather large, thick-walled, arcuate. Peristome 

 large, perfect. 



Readily distinguished from all the preceding genera by the 

 regularly pinnate branching, numerous paraphyllia and curved 

 capsule. The name is derived from Thuja, the coniferous shrub, 

 not from the Greek 9va, and there seems therefore no reason for 

 correcting the spelling as Lindberg does to Thyidium, as there 

 might be were the derivation directly from the Greek. 



Lindberg first pointed out the radical distinction in the apical 

 cells, between the branch-leaves of T. tamariscinum and those of 

 T. recognitum and T. delicatulum, by which these groups of 

 species may be separated at a glance under the microscope ; the 

 difficulty of separating them when barren, and indeed even when 

 fruiting, previously to that time, had caused great confusion 

 between the species, especially in N. America. In T. 

 tamariscinum the apical cell in the branch-leaves ends in a single 

 acute point ; in the other species named it is truncated, with 2-3 

 points or papillae at apex. 



{Stem bi or tripinnate 2 

 Stem simply pinnate 4 



/Apical cell of branch-Is. acute, not divided 4. tamariscinum 



\Apical cell obtuse bifid or ending in a crown of papilla; 5 



/Stem bipinnate ; perichaetial Is. not ciliate 6. recognitum 



^\Stem usually tripinnate; perichEetial Is. ciliate .j. delicatulum 



/Stem-Is. sub-squarrose, strongly auricled .3, decifiens 



4\Stem-ls. not auricled 5 



/Stem rigid ; Is. papillose on keel ; cells shortly oval 1. abietinum 



-■\Stem flexible ; Is. smooth on keel ; cells elongated 2. Blandovii 



1. Thuidium abietinum B. & S. (Hypnum abietinum L.) 



(Tab. L. Q.) 



In loose tufts, often scattered among grass and other plants, 

 dark brown with yellow or green tips; secondary stems 2-4 

 inches long, prostrate or ascending, sometimes forked, rigid, 

 simply and regularly pinnate (very rarely slightly bipinnate), the 

 branches close, sub-equal, not complanate, but in two rows on 

 each side of the stem so as to lie in two planes, slender, short, 

 attenuated at the points ; stem-leaves crowded, spreading when 

 moist or slightly secund, when dry closely appressed and 



