360 C. O. ROSENDAHL 



for several weeks is essential to successful forcing of native 

 perennials. 



The experiment has been carried on for a second time during 

 the present season (1913-1914), partly on the same plants that 

 were used last year, partly on new plants dug and potted during 

 October and November of 1913. 



In view of the fact that slightly different treatment has been 

 employed, the results obtained during the second season are 

 interesting for comparison. 



In the first place, nearly all the plants were obtained later in 

 the season than in the previous year. They were all left out to 

 freeze completely and the freezing period lasted considerably 

 longer than the year before. Finally, the temperature in the 

 forcing house was kept uniformly much higher, ranging from 

 55° to 60°F. at night and often going as high as 80°F. during the 

 daytime. 



In comparing table III with table I it will be noticed that 

 it contains a mmtiber of species not included in the first one and 

 that most of the species used in both cases were the same plants 

 kept over from the previous year. The object of using the same 

 plants again was to determine if a thorough rooting and estab- 

 lishment in the pots and flats during a season of growth would 

 have a beneficial effect on their blossoming. In all cases this 

 proved to be the case, for the plants all grew more vigorously 

 and blossomed more freely than during the previous season. 



That the increased temperature may have been partly respon- 

 sible for this is possible, yet in the light of other facts, it may 

 have been only of secondary importance. On some of the early 

 blooming species the effect of higher temperature was to cause 

 spindling of growth and sometimes impairment of flowering, 

 while on the somewhat later blooming species the effect was bene- 

 ficial in both respects, as was naturally to be expected. In 

 this latitude (45°N.) the temperature that obtains during the 

 time of blooming of Sanguinaria, Uvularia, Hepatica, Dicentra 

 and other spring flowers does not average more than 48°F., 

 whereas the greenhouse temperature maintained in this experi- 

 ment averaged about 20° higher. It is therefore obvious that 



