68 MASSACHUSETTS HORTICULTURAL SOCIETY. 



The plants at the remote end of the rows, although lower and 

 weighing only about four-fifths as much as those near the lamp, 

 produced earlier heads. In other words, the light seemed to 

 produce leaf and stem growth at the expense of heads ; and this 

 rapid growth of the strongly lighted plants was further shown by 

 the much more brittle and tender tissue of these plants. 



Most plants show a similar modification of habit under the 

 immediate influence of the light. As a rule they grow taller. 

 This tallness is ordinarily due to a longer growth, but it is some- 

 times only the result of erectness. Thus on the, seventh of last 

 month, I secured two pots of oxalis, each containing two plants 

 of equal size, and placed one pot eight feet from the lamp and the 

 other forty-five feet from it in diffused light ; and at the same 

 time I took two equal pots containing one plant each and set them 

 in the same positions. Three weeks later there was a marked 

 difference in the two lots, those nearest the light being considerably 

 taller than the others ; yet these tall plants appeared to have made 

 no more growth than the others, for the total growth of one pot in 

 the light was to the corresponding pot in comparative darkness as 

 58 is to 74, while in the other the ratio was reversed, being as 43 

 is to 33. This taller growth was probably a species of heliotropism 

 or growing towards the light, for the artificial light proceeds from 

 a definite point overhead, while the sunlight is much diffused. 



In contrast to this behavior of the oxalis, however, may be 

 cited the case of three equal primula plants without flower Inids, 

 which were selected for experiment the first of January. These 

 were placed together twelve feet fx'om the naked arc. One plant 

 was unprotected, one was screened by a pane of window glass, 

 and the third was covered at night so that it stood in darkness. 

 Four weeks later the plants were in flower with little difl:erence in 

 the earliness of the first blossoms, although the plant screened by 

 the pane was producing more buds than either of the others ; but 

 the plant kept in darkness was much shorter than the other two, 

 *for while each of them stood five and one-half inches high, this 

 was only three and three-fourths inches. 



It is important that we notice the fact in this interesting 

 behavior of the primulas, tliat the fully exposed and the glass- 

 screened plants seemed to be equal in every respect; in other 

 words, the ])aneful influence upon primulas of the electric arc 

 light of 2000 candle-power does not extend twelve feet. This 



