GRAMINEyE (POACE^), GRASS FAMILY 



83 



The grass fruit is called a grain or caryopsis. There is an 

 abundance of starchy endosperm. Sometimes the grain is 

 closely adherent to the palet and lemma, as in most barleys 

 and oats. 



Phylogeny of Grasses. — The history 

 of the evolution of a group of organ- 

 isms is phylogeny. What is the origin 

 of the grasses? Are they primitive 

 forms, the progenitors of such closely 

 related groups as the lihes and other 

 common monocotyledonous plants; or 

 are they a reduced group? By those 

 who hold the latter view, which is 

 more widely accepted, grasses are con- 

 sidered to have come from lily-like 

 plants by a reduction and modification 

 of a number of parts of the flower. 

 Examination of the floral diagram of a 

 typical lily flower is shown in Fig. 31. 

 It has two sets of floral segments (which 

 together constitute the perianth) which 

 alternate, two whorls of stamens, three 

 in each whorl, and a pistil divided into 

 three chambers, hence tri-carpellary. 

 The stamens of one whorl alternate with 

 those in the other; those of the outer 

 whorl alternate with the inner segments 

 'of the perianth. The three carpels 

 alternate with the inner stamens. In 

 Fig. 31 is shown the floral diagram of 

 a grass flower with the rudimentary or 

 missing parts shaded. According to the view that grasses 

 are reduced lilies, there was a reduction in the lobes of 



Pic. 31. — Diagram of 

 A lily flower, and B 

 grass flower showing 

 homologous structures. 

 A, /, bract; ax, axis; 

 op, outer perianth; ip, 

 inner perianth; s, sta- 

 mens; c, tricarpellary 

 ovary. B, shaded struc- 

 tures are aborted; le, 

 lemma (bract) ; ax, axis; 

 p and p', palet (outer 

 perianth); I and I', 

 lodicules (inner peri- 

 anth); i and s', two 

 whorls of stamens; c, 

 tricarpellary ovary. (B 

 after Schuster.) 



