30 Our Native Ferns. 



34. Acrostichum. — In this genus the sporangia are spread in 

 a stratum over the under surface of the upper pinnae in our soli- 

 tary species, but in some exotics they cover portions of the upper 

 surface as well. There is no indusium. 



35. Polypodium. — (Fig. i). This genus contains the largest 

 number of existing ferns, and though all the species agree in the 

 roundish naked sori, the venation is widely different in the various 

 sections which are chiefly formed on the character of the veins. 

 Four of the five sections are represented in our nine species. 



In EupOLVPODiUM the veins are free, yet are occasionally known 

 to unite,* thus indicating a tendency to vary toward the next sec- 

 tion. The sori are generally found at the end of a. free veinlet. 



In GoNiOPHLEBiUM the veins unite near the margin forming 

 large areolae, each containing a single free veinlet which bears the 

 sorus at its end. A tendency to variation is seen in P. incamim in 

 which the veins are free, as well as in P. Californicum in which 

 they are often partly free. 



In Phlebodium the veins form ample areolae in a row next the 

 midvein and frequently in one or more secondary rows, each bear- 

 ing a single sorus at the junction of two or more veinlets. A 

 large number however bear the sori at the end of a single veinlet. 

 From the fertile areolae to the margin the veins anastomose more 

 copiously. 



In Campyloneuron the areolae each usually bearing two sori, 

 are found between the parallel primary veins which extend from 

 the midrib to the margin. 



36. Gymnogramme. — In this genus the sori follow the course 

 of the veins and consequently vary with the venation, being sim- 

 ple, forked, pinnated or anastomose with each other. The sori are 

 non-indusiate. 



37. Notholaena. — In the cloak -ferns the sori are marginal and 

 provided with no indusia. This genus is linked very closely to 

 Gymnogramme on one hand and to some species of Cheilanthes 

 on the other. From the latter it is scarcely separable and the 

 two are likely to be confounded by beginners. 



38. Vittaria. — This peculiar genus occupies a somewhat inter- 

 mediate position between the indusiate and non-indusiate genera, 

 and while usually associated with the latter has considerable claim 

 to be ranked with the former. The fronds are narrow and grass- 

 like, bearing the sporangia in an intramarginal groove, often more 



* Catalogue of the Davenport Herbarium, p. 8. 



