470 Muscologia Itineris Assamici. 



ter of Dicranum, has the peristome of Didymodon, to the 

 former genus. Schwaegrichen however refers a nearly allied 

 species with a similarly anomalous peristome to Didymo- 

 don : this however appears to me to be sacrificing a number 

 of characters to a solitary one. But if such views are 

 correct, my Fissidens neckeroides must be incorporated with 

 Didymodon. 



Fissidens has, I think, without doubt, terminal setae, for 

 in those cases in which they are axillary, they frequently 

 become elongated, which, so far as I know, is never the case 

 with those which have truly lateral setae. Judging from the 

 first developed leaves both of the stem and perichsetium, it 

 would seem that the " duplicatura" of Hedwig is the true 

 lamina, and that they differ only from highly carinate leaves 

 in the excurrent vein being as it were alate, the dorsal ala 

 being prolonged down the carina to its base. The only 

 objection to this view is the frequent inequality of the two 

 lamellae. 



' In Trematadon longicollis, I had opportunities of ascer- 

 taining the correctness of the observations of Mr. Valentine 

 on the development of the setae. With these observations 

 I am only however partially acquainted. The old and 

 incorrect ideas appear nevertheless to still prevail, and are 

 admitted into the second edition of Mr. Lindley's Intro- 

 duction to Botany. The explanations too adopted in this 

 excellent book as to the difference between a mitriform 

 and dimidiate calyptra, and an outer and inner peristome, 

 are likewise particularly erroneous. 



With regard to the development of the setae of Musci, I 

 know of no analogous instances, excepting Jungermannia, 

 which is undoubtedly vaginulate. The changes subsequent to 

 fecundation are, in these, much more complicated than in 

 Phaenogamous plants, in which they are limited almost uni- 

 versally to the maturation of a pre-existing ovule ; whereas 

 in these, they are extended not only to the development of 



