74 MASSACHUSETTS HORTICULTURAL SOCIETY. 



cells, set a young friend of mine, up in the hills of New Hamp- 

 shire to thinking that, possibly, densit}^ of sap or cell contents 

 would do as well, and he tried this experiment. In the fall, when 

 the prospect was rain, with a strong probability that it would be 

 followed by hard frost, he scattered over the ground, about some 

 hills of potatoes, some soluble salts. In a few days came a rain, 

 and that was followed in a couple of days by a frost that killed 

 down all the potatoes, except those in the hills about which he 

 had scattered the salt. His father observed the fresh foliage of 

 these hills among the dead vines, and said he guessed they had 

 mixed the seed in planting. My young friend writes, " I did not 

 tell what I had done, fearing that the ultimate results of the appli- 

 cation might be worse than the frost, and as we had a hard frost 

 the next night, which they did not stand, I lost my experiment." 

 Was he not right in his speculation? Frost injures plants by rup- 

 turing the cells, in the crystallizing of the contained water. Salt 

 water, milk, and cider, do not freeze as soon as clear, fresh water ; 

 therefore, is it not reasonable to suppose that the young plant 

 whose germination began under such favorable auspices, will be 

 better able to resist the late spring frosts, and therefore to start 

 earlier, and will give to its progeny a like habit? It is of the first 

 importance that the young plant should be able to begin its work 

 early in the spring, Vv^hile light and heat are on the increase, as 

 plants appear to grow under an increase, and to mature under a 

 decrease, of light and heat. This influence, of increasing light 

 and heat, is what gives to the morning sun its reputed value over 

 the evening as a stimulant to plant growth. And that which is 

 true of the day, in respect to the sun's influence, is true of the 

 year. Hunt found by the use of glass of different colors, that cell 

 growth was stimulated under yellow light, as we see illustrated in 

 cloudy weather in the spring or summer ; functional activity under 

 red and blue, and maturation under viole't. Gen. Pleasonton's ex- 

 periments confirm Hunt's, particularly as to the value of the blue 

 and violet rays in development and maturation. The violet are 

 the most refrangible of the sun's rays, and the red the least. 

 Owing to this difference of refrangibility, the violet and the blue 

 rays strike the leaf more nearly vertically in the morning and even- 

 ing, than the red rays, and hence the plant is more under their in- 

 fluence at those seasons, and this is the case in the fall, winter, 

 and spring, for the entire day, while the sun is in low declination. 



