496 Mr Compton, On Right- and Left- Handedness in Barley. 



imitate the leaf-margins. The condition with the right margin 

 overlapping is called right-handed ; that in which the left margin 

 overlaps is called left-handed*. 



Leaves subsequent to the first are also twisted : the normal 

 arrangement appears to be that R.H. and L.H. leaves alternate all 

 the way up the stem ; i.e. if the first leaf be l.h. the second will 

 be R.H., the third L.H., and so on. But this rule is subject to 

 frequent exceptions in which the arrangement may be irregular 

 and two or more successive leaves may have the same twist. 

 The frequency of these exceptions, as well as the difficulty of 

 accounting for them, suggest that the characters of right- and 

 left-handedness are largely under the influence of slight "ac- 

 cidental" causes, of whose nature we are ignorantf. 



The fertile axis bears a series of alternate notches in which 

 are inserted the flowers, three to each notch. In six-rowed 

 barley all three flowers set seed ; in two-rowed barley only the 

 middle flower of each group of three. I shall speak of the " odd " 

 and "even" notches in the spike ; the odd being numbers 1, 3, 5, ... , 

 and the evens being numbers 2, 4, 6, ..., reckoning from the base 

 upwards. The first few flowers are usually sterile. 



On flowering the anthers may be extruded, and pollen 

 scattered ; but the flowers do not open, and the stigmas never 

 come outside the glumes. Consequently, self-pollination is 

 regularly effected. Prof Biffen tells me that he has never 

 detected any signs of crossing. It is possible, though not without 

 much difficulty, to perform emasculation and cross-pollination of 

 the flowers : and I have made a few such crosses. The results 

 were meagre, however, and as, for reasons to be explained below, 

 they throw no light on the problem, no further mention Avill be 

 made of them. 



I have worked almost entirely with two-rowed varieties of 

 barley, because some of the manipulation is thereby simplified. 



The following points will be considered : 



* There is never any real doubt whether the seedling is e.h. or l.h. Occasion- 

 ally plants are found in which both margins of the leaf appear to be inroUed : but 

 inspection shows that at the base of the leaf the normal overlapping occurs. Among 

 4000 seedlings 15 such were found. 



In one case a single seed produced on germination two shoots of equal size : of 

 these one had the first leaf e.h. the other l.h. 



The auricles at the junction of leaf-blade with sheath follow the twist of the 

 leaf : that auricle being lower which is on the overlapping margin. 



+ See Stratton and Compton, "On Accident in Heredity," in the present number 

 of these Proceedings, p. 507. 



This overlapping of leaf-margins is entirely different from the rolling of the 

 leaf blades of grasses which is used as a taxonomic character in agriculture. See 

 for example Percival, Agricultural Botany, p. 511, where barley, wheat and rye are 

 said to have the "leaf-blades rolled to the right," while in oats the leaf -blade is 

 " generally rolled to the left." See also Hackel, in Engler and Prantl's Nat. Pfifam. 

 "Gramineae," p. 4. 



