Page:An illustrated flora of the Pacific States (vol. 1).djvu/22



Terrestria, epiphytic, or (rarely) aquatic plants, exhibiting a life cycle of two well-marked phases, Sporophyte and Gametophyte, the so-called alternation of generations. The former is the conspicuous one; the plant, known as a fern or fern ally, s sually differentiated into root, stem, and leaf, is provided with vascular tissues, and bears spores asexually, these either alike (plants homos- porous) or of two very unlike kinds called microspores and megaspores (plants heterosporous). The germinating spore produces the Gametophyte, or minute, inconspicuus sexual stage (prothallium). In the homosporous series the pro- thallia are similar, but may be monoecious or dioecious in the heterosporous series they are dioecious, the ones developing from the microspores producing only male reproductive organs (antheridia), and those from the megaspores only female reproductive organs (archegonia). Fertilization consists in the impregna- tion of an egg cell or archegone by the coiled motile male element (spermatozoid). The resulting growth is the Sporophyte, or conspicuous asexual stage. The pteridophytes first appeared in the early part of the Palaeozoic Era, and reached the height of their development in Carboniferous Time, when they formed the dominating type of vegetation. There are about 7,000 iving species, of which more than three-fourths are restricted to tropical regions.

Sporophytes herbaceous, consisting of a short fleshy rhizome, bearing numer ous fibrous, usually fleshy roots and one or several leaves. Leaves (fronds) erect (in our genera), not jointed, consisting of a simple to variously compound, sessile or stalked sterile blade and, in the fertile leaves, a stalked sporebearing spike or panicle (sporophyll), borne on a short to elongate common stalk. Sporangia developed partly from subepidermal tissue (plants eusporangiate), naked, open- ing by a transverse sli. Spores ufrm (plants homosporous). yellowish. Gametophytes (prothaa) hypogean, tuberlike, usually lacking chlorophyll and associated with an endophytic mycorhiza. Five genera, the two following widely distributed and with numerous species, t ers monotyp Sterile blade simple, with reticulate veins; sporangia united in two rows in a simple, slender, fleshy spike. Sterile blade 1-4 times pinnately divided, with free veins; sporangia globose, all distinct, borne in a spike 2. Botrychium or

Small herbaceous terrestrial plants. Rhizome short, hypogean, usually erect, terminat ing in the erect exposed bud for the following season. Leaves erect in vernation, 1-4, erect glabrous, fleshy, arising at the side of the apical bud; common stalk short to elongate slender; sterile blade simple, sessile or short-stalked, linear-lanceolate to ovate or reniform, with reticulate venation, the areoles simple or with free and anastomosing veinlets sporophyl a simple slender long-stalked spike, the large globose sporangia marginal, coalescent in 2 ranks, transversely dehiscent. [Name Greek, meaning the to alluding to the form of the narrow sporophyl1.] About 45 species, of wide distribution in both hemispheres. Besides the followirn of a snake others occur in the United States. Type s Ophioglossum vlgatum Fronds usually solitary and much more than 10 cm. long: sterile blade obtuse or acutish, 1-5 c Fronds usually two and less than 10 em. long; sterile blade acute, often apiculate, 5-10 mm broad 2. O. californicum. opaque.