126 Phf/siolofjicaf Prr-thtrnniuatioii 



Other investigators who have dealt with the effect on the size of 

 seed of their position on the parent plant in the case of cereals and whose 

 results confirni those of Nobbe may be mentioned. Von Riimker(0;i)i 

 in the case of wheat showed that the heaviest grains on the inflorescence 

 occur on the lower half of the spike while Fruwirth(2i) showed that the 

 heaviest grains of Barley, Rye, Wheat, Spelt, and Maize, are situated at 

 the middle or somewhat below the middle of the ear (cf. also Wenholz («))). 

 Bruyning(fi) found that the lower grains of the lateral ears are the best 

 in the case of oats-. 



Halsted(26) has recently shown that seeds of corn taken from the 

 middle of the ear produce more vigorous plants than those taken from 

 the base, whilst those from the base are better again than those from the 

 tip of the ear. Walls (77) in 1905 found that a strong relationship existed 

 between the size of the germ and the vigour of the resulting plant and 

 that this vigour continued throughout its life-history. He also found 

 that the plants from the grains with the largest germs were better able 

 to withstand drought. 



{(■) Experiments in which the Factors controlling the Size of 

 the Seed are undetermined . 



A large number of experiments have been conducted chiefly with 

 cereals to determine the difference in yield obtained when selected 

 large and selected small seed are used for comparison. The balance of 

 evidence is in favour of the conclusion that more vigorous plants and 

 better yields are obtained by the use of heavy seed. The chief difficulties 

 to be encountered in interpreting these results from the point of view 

 of their significance as evidence of physiological pre-determination lie 

 first in the possibility of hereditary factors for seed-size being concerned, 

 and secondly in the fact that in field experiments on the basis of the 

 data given it is not possible to compare yield per plant. 



In the case of cereals the presumption has usually been that the 

 experimenter is concerned with a hereditary factor, but. as we have 

 already indicated, the fact that the size of the seed appears to be almost 

 entirely controlled by its relative position on the ear militates strongly 

 at the outset against this view. Further, in most experiments continued 

 over several years with continuous selection of large and of small 



' In contrast to VValdron, von Kiimkcr found in the case of wlioat tliat tlu' average seetl- 

 woight increases witli ttie size of (he spike. 



2 As long ago as 1830 Oiroii de Biizareinguos (!)) stated tiiat in tlie iienip tiie largest 

 seeds occur in the middle legion of the iiiHorcsccnce and give rise to the laigest plants. 



