II. The Development of the Ostrich Fern, Ojstoclea struthiopteris. 

 By Douglas Houghton Campbell, Ph.D. 



(Walkei- Prize Essay, 1886.) 



j^MOj^G the most characteristic ferns of the northern United States are those be- 

 longing to the genus Onoclea, represented by three species, two of which, O. sensihilis, 

 L., and O. stvuthioj^teris, Hoffm., are found throughout the northeastern United States, 

 the latter species, the subject of this memoir, being less generally distributed, though lo- 

 cally abundant. It also occurs throughout northern Eurojie and Asia. 



The sporangia in this fern are borne in great numbers on the back of the fertile fronds, 

 and as these remain standing through the winter after the sterile fronds have decayed, 

 spores can be obtained at all seasons of the year. These retain their vitality for several 

 months after being gathered, so that when the plants are common, abundance of material 

 is constantly on hand. This foct, together with the ease with which the spores can be 

 germinated, makes the plant a specially valuable one for study. 



The observations here recorded were begun in the spring of 1882, and were continued, 

 with more or less interruption, through the autumn of 1885. The points of most im- 

 jiortance discussed are the following: 



The presence of a third coat in the spore. 



The marked dioecism displayed b}' the prothallia. 



Formation and development of the apical cell of the prothallium. 



Continuity of the protoplasm in the cells of the prothallium. 



Development of the antheridium and antherozoids. 



Absence of the ventral canal-cell in the archegonium. 



Succession of the divisions of the embryo and the establishment of the apical cells 

 of its different members. 



Development of the different tissues of the embryo. 



Development of the leaf from the apical cell, and the relation of the different tissues 

 of the leaf to the segments of the apical cell. 



Method of formation of the pinnae. 



Development of the stem from the apical cell. 



Development of the sporangium. 



MEMOIRS BOSTON SOC. NAT. HIST., VOL. W. i (17) 



