MANUAL OF THE GRASSES OF THE UNITED STATES 



9 



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 

 2-celled anthers which are basifixed 

 but so deeply sagittate as to appear 

 versatile. The pistil is 1 -celled, with 1 

 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 

 elongated and stigmatic over much of 

 the exserted surface. 



The lodicules are small organs 

 found at the base of the flower outside 

 the stamens. There are usually 2, 

 rarely 3, 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 (Pani- 

 cum 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 (Sporo- 

 bolus, 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 en- 

 closed, as in the oat and in the Pan- 

 iceae. The grain (caryopsis) may en- 

 large during ripening and greatly ex- 

 ceed 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 peri- 

 carp. The part of the caryopsis not 

 occupied by the embryo is the endo- 

 sperm, or nourishment for the ger- 

 minating seed. 



CLASSIFICATION OF GRASSES 



A natural classification of plants is 

 one in which the different kinds or 

 species are arranged in groups ac- 

 cording 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 gener- 

 ally accepted that there has been 

 much variation during the evolution- 

 ary 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 re- 

 mains, but relatively few of the an- 

 cestors of living plants are repre- 

 sented by fossils. Knowledge of the 

 ancestry of the kinds of plants now 

 on the globe is necessarily very in- 

 complete. Hence, ideas of the rela- 

 tions of groups to each other are 

 largely inferences based upon mor- 

 phological resemblances. Those indi- 

 viduals which are so much alike as 

 to appear to be of one kind, with, 

 presumably, a common ancestor in 

 recent geological times, are regarded 

 as belonging to the same species. 

 The species is the unit of classifica- 

 tion. For convenience, species are 

 grouped into genera and genera into 

 families. For example, the white oak, 

 red oak, black oak, and other kinds 

 or species of oak belong to the oak 

 genus (Quercus), all the species of 

 which have one character in common 

 — the fruit is an acorn. The oak 

 genus, the beech genus, the chestnut 

 genus, and a few allied genera are 

 grouped together as a family. 



The grass family (Gramineae or 

 Poaceae) is one of the largest in 

 number of genera and species, and, 



