ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 207 



denoted the physiological constant. The same explana- 

 tion probably holds good for .those rosettes of biennials 

 which develop an inflorescence far in advance of others. Ob- 

 servations on Lactuca Scariola integrata have shown that the 

 rosettes formed early in the fall were the first to bloom dur- 

 ing the following year. 



A smaller amount or a lesser intensity of light seem to cause a 

 delay in the appearance of the flower, a matter of common 

 observation in horticultural establishments. It is shown also 

 by the behaviour of representatives of a species occurring both 

 in the open and in the woods, though in the latter case a lower 

 temperature and increased humidity, both of soil and air^ 

 play a part. That a greater degree of soil moisture, alone 

 or practically alone, delays the flowering period is shown by a 

 comparison of indi\dduals of the same species in dry situations 

 and in moister surroundings. The wet and the dry portions 

 of the American Bottom yield numerous instances. Drought 

 will cause an early appearance of the flower, a fact well known 

 to florists and made use of by them when preparing potted 

 plants for market. 



Phenological phenomena further depend on individual 

 characteristics and state of health of the tree or plant and, 

 as shown in the case of fruit trees, but probably appHcable 

 to other plants also, on the heavy or light fruiting in the year 

 previous to flowering.* Some plants, under apparently 

 identical conditions, vary greatly in respect to flowering sea- 

 sons. Specimens of Hamamelis virginiana, properly flower- 

 ing during the autumn, frequently do so in spring, others, 

 in the immediate vicinity, behaving normally. Some will 

 flower even both in fall and spring. 



Different species are not influenced to the same extent by 

 changes of temperature, giving rise to cases of inversion, i. e. 

 where a species which normally flowers later than another 

 does so earlier. t Again, under proper climatic conditions, 

 plants which in one region are annuals may become peren- 



♦ Sandsten, E. P. Conditions which affect the Time of the annual 

 Flowering of Fruit Trees. Wisconsin Agric. Exp. Sta. Bui. 137 : .7. 1906. 



t Rahn^ L_ Ueber phanologische Inversionen. Ber. Oberhess. Ges. 

 Nat. und Heilk. 21:114. 1882. 



