Bibliographical Notices. 217 



tion between the two being thus reduced to a diiFerence, generally 

 very slight, in the form of the sori, Mr. Brown is of opinion with 

 Dr. Blume that these two tribes cannot be generically separated, and 

 suggests that " the section of Gymnogramma referred to should be re- 

 moved from that genus, and if still distinguished as a genus or sub- 

 genus, might receive the name oiPleurogramma." With this section 

 Meniscium is also manifestly related, as well as that section of Ne- 

 phrodium which M. Gaudichaud has separated under the generic 

 name of Polystichum ; "an approximation which appears to be con- 

 firmed by more than one fern, entirely agreeing in habit, in undi- 

 vided veins and lateral fructification with this group of Nephrodium, 

 but having a short linear sorus with an indusium of corresponding 

 form, inserted by its longitudinal axis in the middle of the sorus." 

 To this group Mr. Brown gives the name of Mesochlana, and ob- 

 serves that " though in general appearance it is abundantly different 

 from Didymochlcena, it can only be distinguished from that genus, 

 according to my view of the structure of its indusium, by its simple 

 veins and lateral sori." Some observations follow on " the most ex- 

 tensive but least natural section" of the genus, in which none of the 

 veins anastomose, and of which Polypodium vulgare is one of the best 

 examples ; and Mr. Brown concludes this branch of the subject by 

 observing : " That subgeneric or sectional characters may in several 

 instances be obtained or assisted from the seeds of this Natural Order 

 is not improbable, and in one case, namely Ceratopteris (or TeleO" 

 zoma), including Parkeria in the genus, even the generic character 

 appears chiefly to reside in the seeds, which in their unusual size 

 and peculiar marking or striation, entirely agree in all the species 

 of the genus, while in the original species the annulus is nearly com- 

 plete ; and in Parkeria, diiFering from the rest of the genus in no 

 other point whatever, the ring is reduced to a few faint striae." 



In another observation on the same fern, bearing m.ore particu- 

 larly on structure, Mr. Brown notices two remarkable points con- 

 nected with the organization of the subgenus to which it belongs. 

 First, " the existence of the complete circle of vasa scalariformia se- 

 parating the ligneous or fibrous vessels of the caudex into an outer 

 and inner portion," which is also found in the caudex of Platyzoma, 

 but not of Gleichenia, and in some (probably in all) of the species of 

 Anemia. Secondly, the production in Polypodium (Dipteris) Wal- 

 lichii, of a gum-like pulpy substance, in which the capsules are im- 

 bedded, even when fully formed, and the remains of which may be 

 found after the spora are discharged. In the dried specimens this 

 pulpy substance had no appearance of organization, but in the living 



