38 ON GENERA AND SPECIES. 



microscopic spores can be made available as auxiliary cha- 

 racters, and tbis will require tbe labour of years ; and even 

 wben 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 

 natural genera and alliances, without requiring much aid 

 from the microscopist. 



Besides the additional characters derived from the struc- 

 ture of the sporangia, both Presl and Fee attach much im. 

 portajice 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 Gyathea arhorea, I found 

 thirty-six vascular bundles in the stipes below the lowest 

 pair of pinnae, and this number nearly corresponded with 

 the number of pinnje 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 pinn» 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 a 

 vascular frame-work, developed according to some definite 

 plan inherent to each individual species, but varying 

 according to the circumstances that influence the growth 



