2070 A TEXTBOOK OF THEORETICAL BOTANY 



Pollination is usually brought about by the wind. In fact the grasses 

 are the most important group with wind-pollinated flowers. Many are self- 

 pollinated, but when hermaphrodite the flowers are often protogynous. At 

 anthesis the stamen filaments elongate rapidly and the light versatile anthers 

 discharge a quantity of fine, granular, smooth pollen through a longitudinal 

 slit which is caught by the expanded stigmas of younger flowers. 



Most species of Wheat are self-pollinated, while some cultivated races 

 of Barley never open their flowers. Cleistogamic flowers are also known 

 among wild species, e.g., Triodia decumbens, Leersia oryzoides and Amphi- 

 carpum purshiit. 



In the embryo sac of some species the antipodal cells begin to divide 

 after fertilization forming a many-celled parenchymatous tissue in the 

 lower end of the embryo sac. The embryo sac grows at the expense of the 

 nucellus of which only one or two layers eventually remain and become 

 filled with endosperm. The embryo has a lateral depression above which 

 develops a terminal structure which finally becomes lateral and shield- 

 shaped, producing the scutellum. The plumule is covered by a sheath 

 formed from the borders of a lateral depression which grows up to form a 

 collar known as the coleoptile. The radicle is similarly protected by a 

 sheath formed by the edges of a cleft in the scutellum tissue. This is called 

 the coleorhiza. Adventitious roots may already appear before the embryo 

 is mature. 



The classification of the family has been the subject of considerable 

 study and there is by no means complete agreement as to the number of 

 tribes into which it should be divided nor as to the distribution of the 

 genera among the tribes. The latest and most detailed account is that by 

 Hubbard, published by Hutchinson in his " Families of Flowering Plants". 

 Here we shall follow that treatment but shall mention only the more 

 important of the twenty-seven tribes there described. 



I. Pooideae 



Spikelets one- to many-flowered, dividing up at maturity above the more 

 or less persistent glumes, or if falling entire, then not two-flowered, with 

 the lower floret male or barren and the upper hermaphrodite, usually 

 laterally compressed or terete. 



This is the larger of the two sub-families and is divided by 

 Hubbard into twenty-four tribes, of which the more important are dealt 

 with below. (For the sub-family Panicoideae see p. 2082.) 



I. Bambuseae. Shrub or treelike, rarely perennial herbs, erect, some- 

 times climbing and usually woody, bearing leaf sheaths with 

 reduced blades which are flat, linear or oblong-lanceolate with 

 petiolar bases and frequently articulated to the sheath. Spikelets 

 (Fig. 2007) all similar, one- or many-flowered. Glumes usually 

 two but sometimes more, outer paleae awnless, five- or many- 

 nerved. Inner paleae either two-keeled, keelless or suppressed. 

 Lodicules three, rarely more or less. Stamens three, six or more. 



