278 LETTER XXIV. 



other in size or number, or arrangement ; some have 

 only 4 teeth, others 8, or 1 6, or 32, or 64 ; in all 

 cases, their number is some multiple of four ; a curi- 

 ous circumstance which shews the great simplicity of 

 desioTi that is observed in the construction of these 



o 



minute objects. The fringe is not, however, always 

 present ; there is a small section of the Moss tribe, 

 all the genera of which are destitute of that singular 

 organ. What office it may have to perform, we can 

 only guess ; it seems to be connected with the dis- 

 persion of the spores, and often acts in the most 

 beautiful hygrometrical manner. If you take the 

 theca of this Tortula, for example, when dry, and 

 put it in a damp place, or in water, its teeth will un- 

 coil, and disentangle themselves with a graceful and 

 steady motion, which is beautiful to look upon. 



It is in the inside of the theca that the spores are 

 confined. They lie there in a thin bag, which is open 

 at the upper end, and which surrounds a central 

 column, called the columella. They are exceed- 

 ingly minute, and not unlike the spores of Ferns. 



A superficial observer would remark no further or- 

 ganization than this ; but the accurate investigations 

 of Botanists, have led to the discovery, that there 

 is a more minute and concealed system of organs, 

 which, in many cases, precedes the appearance of the 

 theca. It has been thought that these organs re- 

 present pistils and anthers of an imperfect kind ; but 

 you will see that, if they are to be so understood, 

 they are so much more imperfect and so differently 

 constructed from the parts that bear those names in 



