176 STEBBINS 



the root-hair emerges from the middle of the cell and at a right angle to the 

 axis of the root. In the Festucoideae, on the other hand, the mature epi- 

 dermal cells in the root-hair zone are of two types, long and short. Only the 



PANICOID 



CHLORIDOID 



FESTUCOID 



BAMBUSOID 



Seedlings 



Leaf 

 X-section 



Leaf 

 epidermis 



Chromosomes 





-'HXC 



$m 



Fig. 3. Chart showing the differences between the four largest subdivisions of the 

 grass family (Panicoideae, Chloridoid-Eragrostoid group, Festucoideae, Bambuseae) 

 in respect to four diagnostic characteristics of the vegetative parts. Individual draw- 

 ings as follows: Seedlings: Paniaim sp., Chloris cucullata, Festuca elatior {all from 

 Prat, 1936); Pleioblastiis Sinioni (from Makino, Flora of Japan). Cross sections 

 of leaves: Panicum dichotomiflornm {original, from preparation by V. I. Cheadle); 

 Eleusine tristachya {from Hubbard, 1948); Lolium perenne {from Hubbard, 1948); 

 Arundinaria argentea striata {original, from preparation by V. I. Cheadle). Epider- 

 mis of leaves: Digitaria sanguinalis {original, specimen from campus. University 

 of California, Berkeley) ; Cynodon dactylon {from campus. University of California, 

 Berkeley) ; Festuca arundinacea {from campus. University of California, Davis) ; 

 Chimonobambusa marmorea {campus. University of California, Berkeley). Chro- 

 mosomes: Panicum eruciforme, Chloris barbata, Lolium. mtdtiflorum, Bambusa sp. 

 {all from Avdulov, 1931). Chromosome drawings all reproduced at a magnification 

 of X980; other drawings at various magnifications. 



shorter cells can give rise to root-hairs. The hairs, furthermore, emerge from 

 the apical end of these cells and project forvi^ard at an angle of about 45 

 degrees with the axis of the root. A speculation worthy of mention, since it 

 could be tested experimentally, is that the method of root-hair development 

 found in the Festucoideae is a specialization adapting these grasses to rela- 

 tively rapid elongation of the roots and assimilation of water and minerals. 



