240 Mr. Valentine on the existence of Stomata in Mosses. 



theca of Encalypta citiata proved its fallacy. Besides, in Encalypta vulgaris 

 I have since observed several similar exceptions ; in the genus Orfhotrichum 

 and in CEdipodium Griffithianum they exist on the upper part of the fleshy 

 seta as well as on the apophysis. In many mosses without apophyses, they 

 are found in a single row at the very base of the theca; for instance, in Tri- 

 chostomum patens and all the Phascums, with the exception of Phascum alter- 

 nifolium, which is destitute of them. Of one hundred and three British spe- 

 cies which I have examined, seventy-eight are furnished with stomata. As 

 yet I have discovered no particular condition which is necessary to their 

 existence; they are found equally on the most fully developed species, as 

 Hypnum rutahulum, as on the very lowest, of which Phascum serratum is the 

 best example ; and, on the contrary, they are wanting in species of both ex- 

 tremes, as for instance, Hypnum denticulatum and Phascum aliernifolium. In 

 appearance they are generally similar to those of the most common form 

 amongst Phsenogamous plants, as represented at Tab. XXI. fig. 10 ; occasion- 

 ally they are so like the surrounding tissue, that the eye would not detect them 

 if they were not the specific object of the examination ; and in several species 

 of Orthotrichum they are particularly prominent. Their number varies in the 

 different species very considerably, being very numerous on some, as Funaria 

 hygrometrica, and as few as four on others, as Weissia controversa. The con- 

 struction of the stomata is for the most part very simple, as in fig. 10, which 

 represents four stomata from the apophysis of Dissodon splachnoides. Each 

 stoma is formed of two oblong reniform cells, with their concave sides op- 

 posed to each other, by which means an aperture is formed in the cuticle. 



Fig. 1 1 . represents a section of one of these stomata. This form appears to 

 be by far the most general, as I have observed only two exceptions. Fig. 1, 

 2, 3, 4, and 6 represent one of these exceptions, which is confined to five of the 

 British species of Orthotrichum ; and fig. 7, 8, and 9 the other, which is pecu- 

 liar to two very nearly allied genera, Funaria and Entosthodon. The first of 

 these exceptions is remarkable, and as far as I can ascertain, not previously 

 described. In addition to the pair of reniform cells, similar to those of Disso- 

 don, the stomata of Orthotrichum diaphanum, pulchellum, rivulare, anomalum, 

 and cupulatum have a raised border of projecting cells, which form a cavity 

 above the stoma, fig. 4 and 5. These projecting cells have the power of con- 



