24 THE LIFE-HISTORY OF A FERN 



In this connection it is well to note further that the spores are produced 

 upon the leaves fully exposed to the air, and that dry circumstances 

 favour the shedding of the spores : Ferns grown in uniformly moist con- 

 ditions show how essential a dry period actually is, for their sporangia 

 often do not burst at all. The spores of Todea and of some Hymeno- 

 phyllaceae may even be seen germinating within the sporangium. Such 



9 St 



Irrn ( 



125 



FIG 



Dispersion of the spores from sporangium of Aspidium acrostichoides, showing different 

 stages of the e version and snapping of the annulus. (After Atkinson.) 



a condition is obviously of no advantage to the plant, and is to be 

 looked upon as a failure in the normal action of the annulus. We thus 

 see that a relatively dry period, such as the Male Fern is able to undergo 

 in summer, is a normal state, and indeed essential for the last phase of spore- 

 production, viz. the dissemination of the numerous living germs. 



But the relatively dry conditions which lead up to and are necessary 

 for the dissemination of the spores do not suffice for their further 

 development : in order that they may germinate moisture is required, 

 as it is also throughout the immediately succeeding stages of life. When 



