GROWTH 211 



ward. Where a very straight root without any contact with moss is desired, 

 it can be obtained by use of a moist-chamber described later under Geot- 

 ropism, but here one must be always on the lookout for Sachs' "curvature," 

 and, as far as possible, should select seeds (e.g., Corn, Horse Eean, Earley, 

 Oats) which do not raise the cotyledons above the ground. 



Where it is desirable to. hasten germination of seeds, it is customary first 

 to soak them. The value, and optimum period, for this soaking for common 

 seeds has been studied somewhat thoroughly in my laboratory by Miss Ecker- 

 SON. She has found that for most seeds a preliminary soaking does mate- 

 rially hasten germination, especially where these are large and are used in 

 the saucer germinator, which of course communicates water to the seeds 

 less readily than does moss or earth. Soaking, obviously, has no value except 

 to hasten access of water to all parts of the seeds, and the sooner the seed 

 is given air after this is accomplished, the better, since longer immersion 

 actually lengthens the period of germination, and, if prolonged, causes irreg- 

 ularities in the seedlings. The optimum period of soaking varies from noth- 

 ing in very small seeds, like mustard, up to twenty-four hours for large seeds 

 like Beans, some of the more important of the intermediate times being, 

 in hours, Radish ±, Barley 3, Buckwheat 3-5, Castor Bean 5, Indian Corn 

 7, Wheat 16. Some of the common seeds (e.g., Oats, Buckwheat, Sun- 

 flower, Tomato) will germinate under water, but most others will not. Some 

 seeds, e.g., Castor Bean, Indian Com, Wheat, String Bean, White Lupine, 

 and Horse Eean, germinate better if the water is changed two or three times 

 while they are being soaked. All of these times are for ordinary room tem- 

 perature, and without doubt they would be shortened if lukewarm water 

 were used. In general, with grains especially, the root end of the seed should 

 be allowed air, no matter if the remainder is immersed; but after the roots 

 have developed they will grow freely, as a rule, even under water. 



An incidental advantage of soaking is that soaked seeds develop fewer 

 moulds than unsoaked, of course, because the soaking removes the spores. 

 Hence when seeds are not soaked, it is well to wash them before use. 

 Methods of growing seedlings without moulds, in aerated test-tubes, have 

 been described by Metcalf and Hedgcock in Journal of Applied Micros- 

 copy, 6, 1903, 2493. Further, immersion for 10 minutes in water kept 

 between 56 and 57° is said to kill smut (and doubtless other Fungi) of Oats. 



A number of simple germination methods, suitable for elementary demon- 

 stration purposes, are described by Loomis in the Nature Study Review,, 

 3, 1907, 200. Compare also E. F. Bigelow's notes in the same journal. 



Any consideration of the effects of heat and light suggests 

 the third leading form of energy, viz., electricity, including mag- 

 netism. Since plants are not exposed to these forces in Nature 

 except in the rare and violent form of lightning, or in the neces- 

 sarily weak form where light plays upon leaves, any effect they 

 have upon growth can only be of an accidental or coincidental 

 character. The practical difficulties in the experimentation, 



