1 20 APLOPERISTOMI. \_Didymodon- 



Didymodon homomallum. Hedw. Sp. Muse. t. 23. f. 1 7. 

 Schwaegr. Suppl v. 1. p. 146. Brid. Meth. p. 102. 



Grimmia homomalla. Smith, Fl. Brit. p. 1194. Enc/l. Bot. t. 1900. 

 Bryum Weissia. Dicks. Crypt. Fasc. 2. p. 5. 



HAB. On the earth in mountainous situations. 



We cannot avoid considering the Didymodon homomallum of 

 Hedwig, Wahlenberg, and Mohr, as not specifically distinct 

 from our D. heteromallum, ( Weissia heteromalla of those au- 

 thors,) although much stress has been laid on the diagnosis by 

 the two latter. Specimens of the former, from the German 

 botanist Ludwig, in Mr. Turner's Herbarium, have the greatest 

 similarity with our plant, differing only in their smaller size, 

 darker colour, and more secund leaves ; nor, indeed, does the 

 figure in Hedwig's Species Muscorum, (TAB. XXIII.) differ 

 in any essential particular. Thus much for the general appear- 

 ance of the two plants, their foliage and capsules. In regard to 

 the peristome, we find both to have 16 long, filiform, oc- 

 casionally perforated teeth, placed in rather distant pairs, so 

 that their approximation is not very easily discoverable ; and 

 hence it has happened that in the figures of what is called 

 Weissia heteromalla in Hedwig's Stirpes, the teeth are repre- 

 sented at equal distances. Wahlenberg appears to have de- 

 scribed, under his Weissia heteromalla, a plant different from 

 ours ; since he says " rarissimus muscus a paucis botanicis 

 visus;" and again, "abunde differt a Didymonte homomallo, 

 foliis brevibus neutiquam arcuatis, sed tantum leviter versus 

 unum latus spectantibus, basi vaginantibus, atque caule subfili- 

 formi longiore;" characters which do not well accord either 

 with our specimens or with Hedwig's figures. Our plant is 

 remarkable for its crowded mode of growth, yellow-green leaves 

 and pale fruitstalks; the latter becoming redder upwards, 

 especially as the plant advances towards maturity. 



Since the first edition of this work was published, we have 

 examined specimens of this moss from Wahlenberg himself, 

 and are more than ever confirmed in our opinion of its identity 

 with Weissia heteromalla. The peristome is exactly similar in 

 both individuals ; the slight variation in the lid, noticed by 

 authors, is assuredly not constant, and though we allow that in 



