SECT. II. REPRODUCTIVE ORGANS. 205 



were even decided, still it would be but of little 

 practical utility to the botanist from the extreme 

 minuteness of the parts, and consequent difficulty 

 of observation, rendering them wholly unfit for the 

 purposes of generic distinction. 



The fruit is, indeed, discoverable individually by Institu- 



c tion of 



the aid of the microscope, consisting for the most generic 

 part of a capsule surrounded by an elastic and dl 



tions. 



jointed ring opening transversely when ripe, and 

 discharging the seed, which is a small and minute 

 globule. But even this has been found insufficient 

 for the purposes of generic distinction, the fruit of 

 almost all the Dorsiferous .Ferns being so nearly 

 alike as to present no essential character sufficiently 

 striking ; and the situation and figure of the aggre- 

 gate mass of fruit as assumed by Linnaeus, being, by By Lin- 

 itself, at least defective.* 



But besides the capsule already described as con- 

 taining the seed, the fructification of the dorsi- 

 ferous Ferns is also generally accompanied with an 

 additional integument, called the Indusium. This 

 is a thin and membranaceous substance covering 

 the groups of capsules till the period of the matu- 

 rity of the seed, each group having its separate in- 

 dusium, originating for the most part in the nerves 

 or veins of the leaf, but sometimes also in the mar- 

 gin. In some plants it is circular, in others longi- 



* Smith's Tracts, p. 21 p. 



