. Our native ferns and their allies : with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns. 26 Our Native Ferns ing an indusium which bears the sporangia on its under surface. 45. Pteris.—(Fig. 6). In this genus, which includes the common brake, the otherwise free veins are united by a fiHform receptacle which bears the sporangia. This „,,,,, «--^—. contmuous margmal Ime of fructi- ,,. ,.....,, ^ Fig. G. l*ierui lonyijolia, L. Enlarged fication IS covered by a membra- segment of pinna showing the vein-like nous indusium formed of the mar- receptacle under the margin
. Our native ferns and their allies : with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns. 26 Our Native Ferns ing an indusium which bears the sporangia on its under surface. 45. Pteris.—(Fig. 6). In this genus, which includes the common brake, the otherwise free veins are united by a fiHform receptacle which bears the sporangia. This „,,,,, «--^—. contmuous margmal Ime of fructi- ,,. ,.....,, ^ Fig. G. l*ierui lonyijolia, L. Enlarged fication IS covered by a membra- segment of pinna showing the vein-like nous indusium formed of the mar- receptacle under the marginal indusium. gin of the frond. (Original.) 46. Cheilanthes.—The lip-ferns found within our limits are unequally divided among four sections, all agreeing in bearing the sori at or near the ends of the veins covered by an indusium formed of the margin of the frond. In Adiantopsis the indusia are distinct and confined to a single veinlet. Our species varies from the typical species of this section and has even been assigned to a separate genus. In EucHEiLANTHES the indusia are more or less confluent but not continuous, usually extending over the apices of .several vein- lets. In Physapteris the ultimate segments are bead-like, and the indusium is continuous all round the margin. Aleuritopteris has the fronds farinose below, and includes a single species somewhat doubtfully assigned to our limits. 47. Cr3rptogramme has dimorphous fronds, the margins of the fertile being closely rolled toward the midvein thus covering the confluent sori. At maturity these open flat in order to discharge the spores. 48. Pellaea has representatives of three sections within our limits all agreeing in possessing intramarginal sori w^hich finally become confluent and form a marginal line covered by an indu- sium formed of the margin of the frond. Chetloplecton includes herbaceous species with visible veins and broad indusia. Allosorus includes coriaceous species having wide indusia, while Platy
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