10 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



The palea is mostly two-keeled and often concave between the keels. 

 It is homologous with the prophyllum. Sometimes the two nerves 

 of the palea are so close together as to appear like a single nerve 

 {Cinna) ; sometimes the two nerves are marginal and widely separated 

 as in rice. The keels may be ciliate (Eragrostis), bearded (Triplasis), 

 or winged (Pleuropogon) . The palea is much reduced or wanting in 

 species of Agrostis. Usually the palea falls with its lemma but in 

 many species of Eragrostis it persists upon the rachilla after the fall 

 of the lemma. 



FLOWER 



The flower proper consists of the stamens and pistil. The stamens 

 are usually 3 but may be 1 to 6, rarely more. The slender filaments 

 bear two-celled anthers which are basifixed but so deeply sagittate as 

 to appear versatile. The pistil is one-celled, with one ovule; the 

 styles are usually 2 but may be 1 or 3 ; the stigmas may arise from a 

 single style or directly from the ovary. The style of Zea is greatly 

 elongate and stigmatic over much of the exserted surface. 



The lodicules are small organs found at the base of the floret outside 

 the stamens. There are usually two, rarely three, the function of 

 which is to open the floret at anthesis by their turgidity. They 

 probably represent much reduced divisions of a perianth. 



Typically the grasses are adapted to cross-pollination, but many 

 species are cleistogamous in part. The axillary inflorescences of 

 some species (Panicum clandestinum and allies, Leersia oryzoides) are 

 enclosed in the sheaths and are self-pollinated. The florets of wheat 

 expand for only a short time, when cross-pollination may take place, 

 but for the most part are self-pollinated. 



The fruit of the grasses is usually a caryopsis, in which the single 

 seed is grown fast to the pericarp, forming a seedlike grain. In a few 

 genera (Sporobolus, Eleusine), the seed is free from the pericarp. The 

 caryopsis may be free from the lemma and palea, as in wheat, or it 

 may be permanently enclosed, as in the oat and in the Paniceae. 

 The grain (caryopsis) may enlarge during ripening and greatly exceed 

 the glumes, lemma, and palea, as in maize and Pennisetum glaucum. 



The embryo lies on the side of the caryopsis next to the lemma, and 

 can be easily seen as an oval depression (the "germ" of maize and 

 wheat). The hilum is the dot or line opposite the embryo which 

 marks the point of attachment of the seed to the pericarp. The part 

 of the caryopsis not occupied by the embryo is the endosperm or 

 nourishment for the germinating seed. 



CLASSIFICATION OF GRASSES 



A natural classification of plants is one in which the different kinds 

 or species are arranged in groups according to their resemblances as 

 shown by their structure, especially (in the grasses and other flowering 

 plants) by the structure of their flowers. The plants of today repre- 

 sent a cross section of the lines of descent from countless generations 

 that have preceded them. It is generally accepted that there has 

 been much variation during the evolutionary process, and that all 

 living plants are genetically connected through their lines of descent. 

 Some of the gaps in present-day knowledge of relationship are filled 

 by fossil remains but relatively few of the ancestors of living plants. 



