128 



Closely following Linnams, Hechvig in the year 1787 com- 

 menced his "Descriptio Muscorum Frondosoruni," a work 

 replete with valuable information, both anatomically and 

 systematic. And from this time Muscology may be said to 

 have assumed the rank of a science. Hedwig, unhappily, did 

 not live to complete his contemplated work. However, he 

 was ably succeeded by his friend and pupil Schwsegrichen, 

 who carried out the original plan, and by whose joint labours 

 we have the admirable work just alluded to. Much more has 

 since been done by Schwartz, and Sprengel, and Hornschuch, 

 and Bridel, and by Bruch and Schimper, and by our own 

 countrymen, Hooker and Taylor. 



Hedwig's arrangement, slightly modified, is that now in 

 use amongst botanists. It is founded principally on the 

 number and form of the teeth around the mouth of the theca. 

 The theca is a little urn-shaped body filled with spores, or 

 seeds. This capsule is produced on the top of a stalk, or 

 seta, as seen in the common Tortula of our walls. On remov- 

 ing the operculum, or lid, we find the mouth of that portion, 

 which contains the seeds, furnished with either a single or a 

 double row of teeth, called peristome ; though in some genera 

 this is absent, as, for instance in Gi/mnostomuiii, Sphagnum, 

 Anictanginm, and in the small group of Phascacece the oper- 

 culum is indehiscent. When present, the peristome is 

 invariably divided into teeth, in number from four to eighty, 

 but always some multiple of four. Another important organ 

 is the Cal//pfra. In a young state, the whole of the seta and 

 capsule is enveloped in a thin film of cellular tissue, called the 

 Calj/ptra ; this organ appears to be hermetically sealed around 

 the base of the seta; and, as the plant advances in growth, 

 it is broken away in the middle, one half being carried 

 upwards, so as to act as an umbrella in protecting the young 

 capsule from damage by rain, while the other portion remains 

 at the base of the seta closely enveloped by the perichcetial 

 leaves. On the enlargement of the capsule, the calyptra is 



