THE FERN BULLETIN 



25 



three types of embryo in this group. In one, repre- 

 sented by Ophioglossum mollucanum, the plant is an 

 annual and develops only a root and leaf and has no 

 stem; in another, represented by our own O. Vulga- 

 tum, a root and stem are produced, followed much 

 later by a leaf ; and in the third represented by the 

 well-known 0. pendulum of the tropics a root, only, is 

 produced, the stem and leaf which the plant bears ap- 

 pearing ultimately from a bud on this root at some 

 distance from the prothallium. It may be added that 

 the prothallia of all these species lack the leaf-green of 

 ordinary fern prothallia and must set up a partnership 

 with a fungus in order to produce a new plant. 



Generic Relationships. — It is a comparatively 

 easy matter to distinguish one species from another 

 when one is dealing only with a few specimens of 

 each, but as the amount of material increases trouble 

 develops, due to the variations that are absolutely cer- 

 tain to occur. It then becomes a very nice matter of 

 judgement to draw the line between closely allied 

 species, if, indeed, any hard and fast line can be 

 drawn. Nor is this difficulty absent from the con- 

 sideration of genera though from the nature of the 

 case, it is only the student of the larger aspects of the 

 science, working with an immense amount of ma- 

 terial, that ever experiences any trouble. Ordinarily 

 we have no difficulty in distinguishing an Asplenium 

 from a Nephrodium, for instance, but if all the plants 

 referred to these two genera were brought together, 

 no novice could place many of the species correctly. It 

 has long been known that Acrostichum and the old 

 Aspidium are closely related, and in a recent publica- 

 tion Dr. Christ reverting to the idea, says : "The con- 



