HIDDEN MARRIAGES 



513 



as they dry they stretch out from the spore ; but on the air becoming moist, 

 they contract, and twist around the spore. If a slide of these spores be 

 breathed upon and then viewed through the microscope, they will be seen 

 to leap about as they dry. Another difference between these and fern- 

 spores is found in their possession of chlorophyll. Fern-spores with few 

 exceptions are devoid of this important substance, and if kept dry will 

 retain their vitality, in some species, for several years ; but chlorophyll 

 will not keep, and unless the spores of Equisetacese are placed under such 

 conditions as to induce germination, they perish within a few days of 

 their dispersion. If the proper conditions are present, germination is very 

 rapid a matter of a few hours only. 



The prothallia are commonly dioecious that is, the archegones are 

 borne on a different prothallium from that which bears the antherids, but 

 a few organs of the opposite sex are often produced at a later date. They 

 are very much longer than broad, and the newest portion is much broader 

 than the old. The less vigorous prothallia are male, the more vigorous 

 female; both are lobed at their anterior margin, but the lobes of the 

 females are long strap-shaped extensions. Both forms are found in 



'. Step. 



FIG. 655. PILLWOBT (Pilularia globulifera). 



this plant grows in such quantities that it might be mistaken for a kind of grass, 

 portion of such a colony is here shown. 



