MOSSES WITH A HAND-LENS 19 



short spinose projections. Peristome of s^ or 64 teeth, short, 

 ■without joints, triangular in cross-section. Columella expanded 

 at the top into a circular membrane, the epiphragm, which is 

 attached to the tips of the teeth, and helps control spore dis- 

 tribution. (See Plate I.) 



The plants of this family are among our most common and 

 conspicuous species, and the student will be sure to fall in with 

 them in his iirst day's study. 



KEY TO THE GENERA. 



1. Capsules square or six-angled Polytrichttm, 



Capsules cylindric 2 



2. Calyptra hairy; leaves not crisped when dry Pogonatum. 



Calyptra not hairy; leaves crisped when dry Catharinea. 



POLYTRICHUM. The Hait-Cap Mosses. 



The Hair-Cap Mosses, called Bird Wheat or Pigeon Wheat 

 in many localities, are the largest and most highly developed of all 

 our mosses, and by reason of their size and common occurrence 

 are familiar objects to nearly every one. Many an old field and 

 meadow is carpeted with the dark rich green of the Common 

 Hair-cap. The farmer, however, votes it a pest, as it often 

 entirely supplants the grass over large areas of meadow. 



The hairy cap that gives this genus of mosses its name is 

 composed of long hairs growing from a little scale-like body, 

 the calyptra proper, at the top of the capsule. 



The Hair-caps, in common with most other mosses, are 

 subject to great extremes of moisture and dryness, and their 

 appearance when dry is very different from what it is when 

 moist, as the leaves fold up against the stem to check the rapidity 

 of evaporation. Some plants that do not produce a sporophyte 

 end in a rosette of highly modified leaves. These are the male 

 plants, and among the leaves of the rosette are numerous 

 antheridia. The male plants of many other dioicous mosses end 

 in a similar rosette. The leaves are large, not bordered, miih a 

 sheathing membranous base and very numerous lamellae occupying 

 the greater part of the width of the leaf above the base, making 

 the central portion of the leaf very dark and dense. Capsules 

 prismatic, four- to six-angled, often nearly cubical. Peristome 

 teeth generally sixty-four. 



Pogonatum is put with the Hair-caps by some authors, but 

 is readily distinguished by the cylindric capsules. In other 

 respects there is very little to distinguish the two genera. 



