340 



MOSSES AND FERNS 



CHAP. 



the growth of the prothallium is exactly opposite to that of 

 the first rhizoid (bi-polar germination), and Kny ^ lays a good 

 deal of stress upon this, as distinguishing Osinunda from the 

 Polypodiaceae ; but it is not at all uncommon for O. Claytoniana, 

 especially, to have the axis of growth of the rhizoid almost or 

 quite at right angles to that of the prothallium, exactly as in 

 the Polypodiaceae. Where the germination is truly bi-polar 

 the exospore is pushed up with the growing prothallium, and 

 appears like a cap at its apex, but if the root-hair is lateral, 

 the exospore remains at the base. 



In O. Claytoniana there are usually several transverse walls 



B. 



Fig. 170. — O sinjiiida cinnamomea {L.'). A, Young prothallia ; B, an older prothallium, X260. 



formed before any longitudinal ones, but in O. cinnamomea 

 and O. regalis it is quite common to have the first 

 transverse wall followed by a longitudinal wall in each cell, so 

 that the four primary cells are arranged quadrant-wise (Fig. 

 170, A, c). Rarely the first wall in the prothallial cell is 

 longitudinal, as is often the case in Equisetum, and sometimes 

 the first divisions are in three planes, so that a cell mass is 

 formed at once, as so often occurs in the Marattiaceae. Where 

 a filamentous protonema is formed, a two-sided apical cell is 

 soon established in exactly the same way as in Onoclea. Where 



1 Kny (5). p. 12. 



