CYTOGENETICS AND EVOLUTION OF THE GRASS FAMILY 1 67 



cultivated crop species so that hybrids between them can be obtained. By- 

 back crosses or introgression from such hybrids, the gene pool available to 

 the cereal or cane breeder can be enlarged to include extra genes for vigor, 

 disease resistance, and such valuable qualities as high protein content of the 

 grain. Breeders of forage grasses are trying out interspecific hybrids as a 

 means of obtaining greater vigor, as well as resistance to drought, cold, or 

 unfavorable soil conditions. Specialists in lawn and turf management find 

 that an understanding of grass taxonomy is most helpful to their work. For 

 all these purposes, the most useful system of classification is one which re- 

 flects as nearly as possible the true genetic and evolutionary relationships of 

 the species concerned. 



A second reason for the changing grass taxonomy is that grasses are diffi- 

 cult for the taxonomist. In the words of Edgar Anderson, they are "stream- 

 lined." Their leaves are all alike in shape, and their stems vary relatively 

 little in branching pattern. Their flowers are so reduced that the calyx and 

 corolla, though probably present in the form of small scales (palea and lodi- 

 cules), are very hard to study, and their ovary is reduced to a simple, 

 1 -seeded caryopsis. An amateur in systematic botany who has not tried to 

 recognize the genera and species of grasses could visualize the plight of 

 the grass taxonomist if he should try to place into genera and species a large 

 number of specimens of, say, the rose family which he had mutilated by cut- 

 ting off all the flowers at the summit of their pedicels and trimming the 

 leaves down to a narrow ribbon. If he did this, he would find his attention 

 becoming focused on the inflorescence, particularly the pattern of its branch- 

 ing and the shape of the reduced leaves or bracts which subtend the branches. 

 These are exactly the characters which grass taxonomists have traditionally 

 emphasized. 



The near revolution which is now taking place in grass taxonomy began 

 when a few anatomists like Grob, Duval- Jouve, and Pee-Laby began to 

 examine and compare the leaves of grasses under the microscope. They found 

 that the smooth surface of the grass epidermis, so plain to the naked eye, 

 appears under the microscope as a mosaic of highly distinctive cells: siliceous 

 cells, parenchyma cells, hairs of various types, and specialized cells sur- 

 rounding the stomata. An equal diversity of cells and tissues can be seen on 

 examining a grass leaf in cross section. Furthermore, these cell patterns 

 are characteristic of a species, and often diagnostic also of genera and tribes. 

 But when grasses are classified on the basis of these anatomical characteristics, 

 the arrangement of genera which emerges differs strongly from the classical 

 system based upon characteristics of the inflorescence. It is perhaps for this 

 reason that grass taxonomists paid little attention to these anatomical studies. 

 But in 1931 there appeared the first important work on the cytology of 

 grasses, the monumental treatise of the Russian cytologist Avdulov. He 

 found that if one classifies grasses on the basis of the number and size of 



