FERNS. 195 



them, and then to consider briefly the uses for ferns, to offer some 

 suggestions for making selections for purposes of cultivation, and 

 to point out some of their special characteristics and requirements. 



I have here some fronds of Asju'dium Boottii, a fine, partially 

 evergreen fern, which was first discovered by that excellent 

 botanist and courteous gentleman, William Boott, an honored 

 meml)er of this Society, and named for him by Professor Tucker- 

 man. 



If we examine the backs of these fronds we shall find them to 

 be covered with numerous dark dots collected into groups, each 

 group consisting of a number of small, round, or oblong, capsules 

 borne on minute stalks. 



These capsules, which are somewhat analogous to seed vessels, 

 though morphologically very different, — are technically called 

 sporangia, and are the spore-cases of ferns, being filled Avith 

 spores which are the germinating agencies b}^ which ferns are 

 reproduced. 



Each group, or cluster of sporangia is called a sorus, and, 

 collectively, the clusters are called sori, — meaning the fruit dots. 



If Ave examine such ferns as our present one before they have 

 fully matured their fruit we shall find the sori protected b}' a 

 special membraneous covering, or shield, which is technically 

 called an indusium. Ferns having indusia covering the sori are 

 called indusiate ferns, and those without are called non-indusiale 

 ferns. 



The presence or absence, and sometimes the form, of the 

 indusium, gives generic distinction to different groups of ferns, 

 and their division and sub-division into sections and species is often 

 based on the character of the indusium alone. 



It is now proper to state that the fruitage of a fern plant is to 

 be found collected in the clusters of sporangia, either on the 

 under surface of leafy fronds, like our present one, or in spike- 

 like racemes at the top of distinct stalks partially separated from 

 the leafy portion, as in Osmundu regnlis, or wholl}' so, as in the 

 Ostrich fern and our common Sensitive fern. Ferns like these 

 last are said to be dimorphous, ?. e., having two distinct kinds of 

 fronds. But in all cases, however much the different kinds of 

 ferns may and do vary in their manner of producing sori, the 

 sporangia are filled when mature with a fine almost impalpable 

 powder, which a microscopical examination shows to be composed 



