238. - ON GENERA AND SPECIES. ` 
microscopic spores can be made available as auxiliary cha- ` 
racters, and this will require the labour of years ; and even. : 
when complete, will be of but little service either to the - 
student or general observer; for I am satisfied that, with — 
our present knowledge of the more obvious outward , 
features that distinguish Ferns from one another, these in- - 
teresting plants can be readily arranged in groups forming 3 
natural genera and alliances, without requiring much aid — 
from the mieroscopist, 
Besides the additional characters derived from the struc- 
ture of the sporangia, both Presl and Fée attach much im- ` 
portance to the difference in the number and forms of the ` 
bundles or plates of vascular fibre in the stipes. My ` 
observations upon that point tend to show, that, although 
the bundles are generally uniform in simple fronded spe- 
cies, yet in many others the number and form appear to 
vary according to the frond being more or less compound 
and varying in size, age, and vigour of growth of indi- 
vidual plants of the same species. In the stipes of a full. 
sized frond (ten feet in length) of Cyathea arborea, I found 
thirty-six vascular bundles in the stipes below the lowest 
pair of pinnz, and this number nearly corresponded with 
the number of pinnæ forming the frond ; in fronds of in- 
termediate sizes the bundles were fewer, apparently formed 
suited to the more or less compound development of the 
frond consequent on the size and age of the plant; for 
instance, in fronds of the same Species, a foot in length 
with few pinnæ has only three broad vascular plates in 
the stipes. It is reasonable to suppose that the shape or 
-~ Outward form assumed by every species is based upon 
~ vascular frame-work, developed according to some definite ` 
. plan inherent to each individual species, but varying 
according to the circumstances that influence the growth 
