10 ARKIV FÖR BOTANIK. BAND 1. 



synonym for Trich. jjunctatum Poir.; the »2ntsill'um Sw.» is taken 

 in the same sense as by Hooker and Baker, which I think 

 is a mistake, which has for a long time kept the commonest 

 Sonth American species and forms of this genus in confusion. 



In the list of names by R. Sadebeck in Engler und 

 Prantl, Die natürlichen Pflanzenfamilien, Teil 1, Abteil. 4, 

 1899, p. 104, the confusion of the old species is not improved, 

 the names repians, pusillum and quercifolium being still 

 used in tlie same sense as hy Hooker and Baker, several 

 polymorphous species (as nmscoidcs Sw., quercifolnwi and 

 Kraussii Hook, et Grev.) being left without sufficient points 

 of identification or proper bounds. 



As these plants doubtless are still difficult to distinguish, 

 I think it would be useful for collectors to have some short 

 notes about the commonest species, with exact illustrations, 

 showing the shape, size, veins, and cellular structure on the 

 same enlarged scale. It is evident, that in cellular plants, so 

 like the mosses as these, we can not dispense with microsco- 

 pical inspection, and our knowledge of such species will be 

 very vague, or even incorrect, with only a macroscopical 

 view. In fact, not only has the microscope proved, that 

 there are diff'erences in the shape and size of the cells, which 

 deserve special attention, as already stated by several au- 

 thors,^ but a certain enlargement is also absolutely necessar}-. 

 if the veins are to be clearly seen and illustrated. 



Through the neglect of this rule, so many recent descrip- 

 tions of new species of Didymoglossum are made useless. 

 There are South American species recently described by G. 

 S. Jemnan, for instance setiferuni (Baker), lahiatum, fruficn- 

 Josiim, Fraseri, and others; but without seeing the original 

 specimens, it is quite impossible to understand their relation 

 to known species, or to apply such a name to a plant ga- 

 thered in other places in the future. I do not doubt that the 

 author has described these plants accurately from living spe- 

 cimens, but in most cases, where exact marks are wanted for 

 the purpose of identifying a species without any hesitation. 



^ Tan den Bosch, Hymenophyllaceae Javanicae, 1861, p. 3, says in 

 speaking on this subject: »Si quis objioiat, paruiu commodam in speciernm 



determinatione esse microscopicam investigationem , ei respondere velini. 



rem non aliter sese habere in caeteris plantis lellularibus. in excursu non tuto 

 vel omnino non determinandis > 



