KEY TO THE ORDERS.^ 



I. Plants without flowers or seeds, but producing spores each of which, on germination, develops into 



a flat or an irregular prothallium. The prothallia bear the reproductive organs (antheridia and 

 archegonia). As a result of the fertilization of an egg in the archegonium by a sperm produced in 

 the antheridium a fern or an allied plant is developed. 



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I. PTERIDOPHYTA. 1 



Leaves with broad entire or dissected blades. (Fern-like plants.) 

 Spores of one kind, minute. 



Vernation straight or inclined: prothallium subterranean, yellowish. 



Order Ophiogloss.^les. 1 

 Vernation circinate: prothallium terrestrial or epiphytic, green. Order Filicalbs. 3 



Spores of two kinds, minute microspores and larger megaspores, borne in sporocarps. 



Order Salviniales. 24 

 Leaves scale-like or awl-like. (Moss-like or rush-like plants.) 



Sporangia in an apical cone, borne under peltate scales: stems hollow, rush-like. 



Order Equisetales. 26 

 Sporangia in the axils of small or leaf-like bracts: stems solid. 



Leaves narrow or scale-like, flat, borne on erect or creeping stems: terrestrial plants. 



Order Lycopodiales. 27 

 Leaves awl-like, often much elongated, borne on a short corm-like caudex: aquatic plants. 



Order Isoetales. 30 



II. Plants with flowers which produce seeds. Microspores (pollen-grains) borne in microsporangia (anther - 



sacs) develop each into a tubular prothallium; a macrospore (embryo-sac) develops a minute pro- 

 thallium, and together with the macrosporangium (ovule) in which it is contained, ripens into a seed. 



II. SPERMATOPHYTA. 31 



Ovules and seeds borne on the face of a bract or a scale: stigmas wanting. Class 1. Gymnospekm.^^e. 



Ovules and seeds in a closed cavity (ovary) : stigmas present. Class 2. Angiospermae. 



1. Gymnospermae. 



Plants growing by a single terminal bud, with pinnate leaves circinate in vernation: embryo pro- 

 longed into a spiral. Order Cycadales. 32 



Plants growing by lateral as well as by terminal buds, with scale-like, flat or needle-like leaves not 



circinate: embryo not prolonged into a spiral. Order Pinales. 32 



2. Angiospermae. 



Cotyledon 1: stem endogenous. Subclass 1. Monocotyledones. 



Cotyledons normally 2: stem exogenous (with rare exceptions). Subclass 2. Dicotyledones. 



1. Monocotyledones. 



Perianth rudimentary or degenerate, the members often bristles or mere scales, not corolla-like, or 

 wanting. 

 Flowers not in the axils of dry or chaffy bracts (scales or glumes) . 



Perianth of bristles or chaffy scales. Order Pandanales. 38 



Perianth fleshy or herbaceous, or wanting. 



Fruit baccate: endosperm present. Order Arales. 225 



Fruit drupaceous: endosperm wanting. Order Naiadales. 39 



Flowers in the axils of dry or chaffy, usually imbricated, bracts (scales or glumes). 



Order Poales. 48 

 Perianth of 2 distinct series, the inner series usually corolloid. 



Gynoecium of distinct carpels. Order Alismales. 40 



Gynoecium of united carpels. 



Endasperm mealy. Order Xyridales. 231 



Endosperm fleshy, horny or cartilaginous. 



A. Ovary, and fruit, superior. 



a. Herbs, or rarely shrubs or trees, with simple leaves: ovules 2-many in each cavity of 



the ovary, or solitary only in the case of a few herbs. 

 Inflorescence not a fleshy spadix. Order Liliales. 247 



Inflorescence a fleshy spadix subtended by a spathe. Order Arales. 225 



b. Trees or shrubs, with pinnately or palmately compound or lobed leaf-blades: ovules 



solitary in each cavity of the ovary. Order Arec.^les. 221 



B . Ovary, and fruit, wholly inferior or half-inferior. 

 Endosperm present and usually copious. 



Flowers regular: androecium not reduced. Order Amaryllidales. 285 

 Flowers very irregular: androecium much reduced and modified. 

 Order Scitaminales. 306 



1 Prepared with the assistance of Dr. P. A. Rydberg. 



vii 



