1914] ATWOOD—GERMINATION OF AVENA 380 
the seed coat; (3) enzyme studies. In the studies of factors 
external to the embryo, CrocKER (17, 18) found the seed coat 
obstructs in various cases the entry of oxygen or water. A. J. 
Brown in a study of Hordeum (9, 10) found that non-living struc- 
tures inclosing the embryo have the power of excluding various salts 
and acids in solution. This work was extended by ScHRODER (59) 
for wheat; while REICHARD (57) would explain this peculiarity 
for barley by saying that there is a causal relation between the 
solubility of the tannins in the seed coat by various agents and 
the ability of these agents to penetrate the seed. Wounding and 
its effect on germination has been noted by various investigators 
(12, 17, 30, 31, 39, 41, 65). The germination rate of A. fatua has 
been increased by alternations of moisture and dryness (51). 
Other factors concerned with germination of seeds as so far studied 
are drying (3, 41, 67), freezing and thawing (23, 53, 54), effect of 
urying in soil (4, 21), subjection to various gases during storage 
and germination (41), effects of light (25-28, 35, 36, 43-47), of 
treatment in hot water (5, 41), and in dilute acids (22, 24). 
Chemical and physical studies have been made of alterations 
in the endosperm or embryo of various seeds. H. T. Brown (13) 
believes that in after-ripening of barley cytase, acting on the middle 
lamellae of the cell walls, changes the earlier glazed condition of 
the endosperm to a mealy structure, following which better germi- 
nation is possible. JOHANNSEN (39) correlates after-ripening with 
fluctuations in the sugars and amide nitrogen stuffs, while ZALESKI 
(68) has followed the ripening process of peas and found protein 
increases at the expense of amino acids, amides, and organic bases. 
KressLinc cites work (41) emphasizing the relation between the 
protein content in grasses and the speed of germination. 
The third type of germination studies, dealing with enzymatic 
relations, includes a large number of researches. Brown and 
Morris (12) in their study of Hordeum believe that the develop- 
ment of amylo-hydrolytic enzymes is located in the epithelial cells 
of the scutellum, and think the zymogens of the resting seed on 
germination are activated by the development of acidity. In this 
view as to the function of acidity in relation to enzymes, they 
follow the ideas of GREEN (29). In 1892 HorTerR (37) expressed 
