1 6 OUR NATIVE FERNS AND THEIR ALLIES. 



itidusium covering a single sorus. The veins extend nearly at 

 right angles to the midvein, are free, and usually forked. 



46. Camptosorus. The walking-leaf has oblong or linear 

 indusiate sori, which are irregularly scattered and borne partly 

 on veins parallel to the midvein, and partly on those that are 

 oblique. Those near the midvein are single, those toward the 

 margin are often approximate in pairs and often form crooked 

 lines. The veins are everywhere copiously reticulated. 



47. Phegopteris. In this genus the sori are round and 

 naked as in Polypodium, with which this genus is sometimes 

 united. The sporangia spring from the back of the veins in- 

 stead of the apex, as in the latter genus, and the veins are free 

 except in the GONIOPTERIS, in which they are more or less 

 united. 



48. Dryopteris is largely represented in our limits by two 

 well-marked sections, which are sometimes regarded as distinct 



genera, and two others with characters scarcely 

 less distinct, containing each a single species. 

 In all the sori are roundish, and borne on the 

 back of the veins or rarely at their apex. In 

 NEPHRODIUM the indusium is cordato-reni- 

 form or orbicular with a narrow sinus. This at 

 first covers the sorus and is attached by its mar. 

 gin, but later bursts away at the margin but re- 

 mains attached at the sinus. In some species 

 in this section the indusium becomes shrivelled 

 before the fruit matures, and in this condition 



FIG. 8. Under . , 



sideof a fertile seg-- might be mistaken for a non-mdusiate species 



mentof Dryopteris /tr 1 - o\ 

 filix mas, with ( Fl g- 8). 



mdusium!' M'agni 6 In PoLYSTiCHUM the indusium is orbicular 

 fied. (After Sachs.) and peltate, being fixed by the centre ; the veins 

 are free, as in NEPHRODIUM. 



In CYRTOMIUM the indusium is the same as in POLYS- 

 TICHUM, but the veins tend to unite near the margin, while in 

 ASPIDIUM the veins anastomose copiously. 



49. Nephrolepis has roundish sori borne at the apex of 

 the upper branch of a free vein, near the margin of the frond. 

 The indusia are usually reniform, fixed by the sinus or base, and 

 open toward the margins of the pinnae. 



50. Cystopteris. The bladder-ferns take their popular 



