256 



SEEDLESS PLANTS 



485. — Part of 

 a fertile pinna of 

 polypodlum en- 

 larged, showing 

 the sori without 

 indusium. 



the fronds or pinnae bearing them are said to be fertile. 

 Are there any differences of size, shape, etc., between the 

 fertile and sterile fronds of your specimen? 

 Between the fertile and sterile pinnas ? On 

 what part of the frond are the fertile pinnae 

 borne ? Notice the shape and 

 position of the sori, and their 

 relation to the veins, whether 

 borne at the tips, in the forks, 

 on the upper side (toward the 

 margin) or the lower (toward 

 486.— Part of the midrib). Look for a deli- 

 a pinna of peiUa ^ate membrane iindusimn) 



enlarged, showing . ... 



indusium formed covermg the sori, and observe 

 by the revoiute j^g shape and mode of attach- 



margin. zt^ 1 • 1 



ment. (If the specimen under 

 examination is a polypodium there will be no indusium ; 

 if a maidenhair {^Adi- 

 antum), or a bracken 

 {Pteris'), it will be formed 

 of the revoiute margin 

 of the pinna.) In lady 

 fern {Asplenium Filix- 

 fcemina), and Christmas 

 fern {Asfiidium), the sori 

 frequently become con- 

 fluent, that is, so close 

 together as to appear like 

 a solid mass. Sketch a 

 fertile pinna as it appears under the lens, bringing out 

 all the points noted. 



487, 488. — Christmas fern {Aspidium) : 

 487, part of a fertile frond, natural size ; 488, 

 a pinna enlarged, showing the sori confluent 

 under the peltate indusia. 



363. The Spore Cases. — Look under the indusium at 

 the cluster of little stalked circular appendages (Fig. 483). 

 These are the sporangia, or spore cases, in which the 

 reproductive bodies are borne. Seen under the micro- 

 scope each sporangium looks like a little stalked bladder 

 surrounded by a jointed ring (Fig. 484). At maturity the 



