ON GENERA AND SPECIES. oF 
up in the work. He classifies the genera under twenty-six 
heads, which bear the name of the leading genus of each, 
and adopts the different modes of venation and character of 
the sori as part of his generic character, but he introduces 
new elements in characterising his genera, such as giving 
the form and structure of the sporangia, and the number 
of articulations of the ring, also the different form of 
the spores; these form an important feature in his generic 
as well as in his specific characters; but with regard to 
their value, I candidly confess that in all my observations 
and experiences I have failed to satisfy myself that either 
the number of articulations of the ring, or the form of the 
Spores, can in any way be practically serviceable for 
defining either genera or species. The little value of such 
characters become obvious on comparing his descriptions 
of individual species with their respective generic cha- 
racters, for example, in the generic character of Aspidium 
the number of articulations of the ring is stated to be 
18.20, that is, all his species of Aspidium should not have 
. less or more than the above number; but in ten of his 
new species of Aspidiwm, he describes the number of 
articulations as much below the number assigned in the 
character of the genus; hence, these species according to 
his own descriptions, should not be placed in Aspidiwm. 
. As far as regards the characters derived from the spores, 
lam sensible that their forms are various and in some 
cases peculiar; but the spores of Ferns, like the seeds of 
Other plants, will, if gathered before they are mature, 
appear to the microscopic observer to be normal, and 
figures of such appearances are consequently drawn and 
published, In my opinion much examination is still re- 
ied, before either the structure of the sporangium or 
shrivel and assume forms that will, in many instances, 
