238 



NATURE-STUDY REVIEW [16:6— Sept., 1920 



toothed on the margins. Examining them underneath, we find 

 on each a double row of circular raised dots which are the fruit- 

 dots, or sori ; there is a row between the midrib and margin on each 

 side, and also a double row extending up into the point at the base. 

 Early in the season these spots look like pale blisters, later they 

 turn pale brown, each blister having a depression at its center; 

 . • by the middle of 



June, masses of 

 tiny globules, not 

 larger than pin 

 points, push out 

 from beneath 

 the margins of 

 these dots. The 

 blisterlike mem- 

 brane is simply a 

 cover for the 

 growing spores, 

 and is called the 

 indusium; by 

 July it shrivels 

 into an irregular 

 scroll, still clinging to the pinnule by its depressed center; and 

 by this time the masses of tiny globules cover the entire under side 

 of the pinna like a brown fuzz. If we scrape off some of this fuzz 

 and examine it with a lens, we can see that it consists of numberless 

 little globules, each with a stem to attach it to the leaf; these are 

 the spore cases, or sporangia, each globule being packed full of 

 spores which, even through the lens, look like yellowish powder. 

 But each particle of this dust has its own structure and contains 

 in its heart the living fern-substance. 



Not all the fronds of the fern clump bear these fruit-dots. The 

 ones we select for decoration are usually the sterile fronds, for the 

 fertile ones are not so graceful, and many ignorant people think 

 the brown spore-cases are a fungus. 



i . Fertile leaflet of Christmas fern showing indusia 

 and spore-cases. 2. An indusium and spore-cases, en- 

 larged. 3. A spore-case, enlarged. 4. A spore-case 

 discharging spores, enlarged. 



