146 



PLANT STKDCTUEES 



the stalk again, like a meridian line about a globe, is a row 

 of peculiar cells with thick walls, forming a heavy ring, 

 called the ananlus. The annulus is like a bent spring, 

 and when the delicate wall becomes yielding the spring 

 straightens violently, the wall is torn, and the spores are 

 discharged with considerable force (Fig. 131). This dis- 



FiG. 126.— The purple cliff brake (P^VAfv? atrojmrpj/r^a), showing general habit, and 

 at a a sint^le leaflet showing the dichototnoiis venation and the infolded margin 

 covering the sori. — After JIarion Satterlee. 



charge of fern spores may be seen by placing some sporangia 

 upon a moist slide, and under a low power watching them 

 as they dry and burst. 



Within this sporangium the archesporium (see § 66) 

 consists of a single cell, which by division finally produces 



