ON GENERA AND SPECIES. 65 
older or more perfect fronds of the plant, or different 
plants of the same species, i& is anastomose. In some 
cases, however, the normal structure of the venation is 
partly anastomose and partly free, as in the genera Goni- 
opteris, Nephrodium, Hemitelia, &c. In these genera the 
lower or basal venules of each parcel are anastomose, 
while the upper are free. In some genera, such as Adian- 
` tum, Lindsea, and Asplenium, the venation is normally 
free ; anastomoses occasionally occur in different segments. 
of the same frond, but such seem more accidental than 
normal. 
From what I have now stated it will be seen that neither 
_ the form or position of the sori or venation, the absence or 
presence of indusium, taken singly or combined, can be 
depended on for determining natural genera. Such being 
the case, and haying had under my notice examples of 
clusion that in order to form natural genera the different, 
modes of growth must be taken into account, that is the 
manner in which the developing axis (caudex) increases, 
its direction, and the mode of evolution and attachment of 
modes of growth, which are comparatively as distinct as 
Exogens are from Endogens. My views on this subject 
first appeared in the “ Botany of H. M. S. Herald,” pub- : 
all engaged in the study of Ferns, I will repeat the d = 
stance of what is there given. fo 
Tf Pp olypodium vulgare be examined, it will be seen cna 
3 fronds are produced singly from the sides of a creeping - 
ogressing stem, which has its accrescent apex always in. 
lvance of its young developing frond, each successive frond us 
nearly 1,000 species of living Ferns, has led me to the con- — 
the fronds. I find that Ferns present two very distinct ` ` 
lished in 1853, but as that work may not be accessible to — 
e peines singly from gé. nodes GC at more or. 3 
