181 



mature organ. In Orthotriclmm draphanum, when mature, 

 they are from 20 to 25 ; whilst in the young theca Mr. 

 Valentine has found as few as five. They are very numerous 

 on the apophysis of Funaria hygrometrica. The common 

 form of stoma much resembles the same organ found amongst 

 phaenogamous plants, usually consisting of two oblong reniform 

 cells, with their concave sides opposed to each other. In 

 Funaria hygrometrica they are formed of a single cell in the 

 form of a hollow ring ; and in five British species, Orthotri- 

 clmm, (draphanum, pulchellmn, rivulare, anomalum, and 

 cupulatum,) examined by Mr. Valentine, they have a raised 

 border of projecting cells, which form a cavity above the 

 stoma, resembling somewhat those of Marchantia and Targonia. 



Hairs appear to be of rare occurrence amongst the Mosses, 

 and when found, are confined to the calyptra. In all the true 

 Polytricha, they are most abundant, and are exceedingly beau- 

 tiful; being composed of long jointed tubes. In most species 

 of Orthotricha they are also plentiful. 



The power of expansion and contraction, according to the 

 state of the atmosphere, is almost universally possessed by the 

 Mosses. This is observable in all the species furnished with a 

 peristome. The use of this organ appears to be to protect the 

 sporules from damage or decay ; to which purpose it is most 

 admirably adapted, as in dry weather it opens and scatters the 

 sporules far and wide, whilst in wet weather it contracts, and 

 closes up the mouth of the capsule to protect these delicate 

 bodies from the rain or dew.* 



The seta of our native plant, the Funaria hygrometrica, so 

 common on walls in this neighbourhood, affords a most striking 

 example of the hygrometric property of the Musci. The pe- 

 culiar structure of this plant has been most fully described by 

 Dr. Lancaster, in the 4th vol. of the Annals of Natural History. 



* Hooker, however, in his Botanical Miscellany, vol. I., p. 157, mentions one 

 exception to the general rule, in Brachymenium pulchrum ; in which " the outer 

 teeth spread out horizontally, contrary to what is usual amongst Mosses." 



