8 



tend to better the quality of seed in dense stands, such as more 

 favorable conditions for pollination and the moderating effect of 

 close crown cover, described in the following paragraph: 



The highest quality of seed is produced in dense stands. The germi- 

 nation for open, medium, and dense stands is 70 per cent, 69 per 

 cent, and 79 per cent, respectively. The difference between the open 

 and medium stands is too small to establish any conclusion one way 

 or the other; but the difference in favor of the dense stand is very 

 pronounced. At first thought one might expect to find the highest 

 quality of seed in open stands where light conditions are most favor- 

 able. There are, however, a number of factors which tend to explain 

 why the contrary is true. First, it is obvious that the denser stands 

 afford the best conditions for pollination; secondly, the moderating 

 effect of a close crown cover upon temperature and evaporation 

 would favor seed development, especially in the early stages. Many 

 young cones die during the winter and spring, probably as the result 

 of the unseasonable freezes and the drying winds which are very 

 prevalent. Flowers suffer in the same way. Instrumental observa- 

 tions at the Fort Valley station show that the minimum temperatures 

 under a fairly close canopy are commonly from 3 to 17 higher, and 

 the wind movement and evaporation from 50 to 100 per cent less 

 than in the open. 



That the age and condition of the tree apparently have no mate- 

 rial effect upon the rate of germination is evinced by the fact that 

 the ratio between the germination per cents of different tree classes 

 remains practically constant throughout the period of the test. 



YIELD. 



No accurate data with regard to the absolute yield in seed are 

 available, but a rough measure of this yield is expressed by the 

 production of cones given in the preceding table. It should be 

 remembered that, in comparing yields with a view to determining 

 the influence of the character of the tree ; it is necessary to consider, 

 in addition to the condition of soundness and general health, also the 

 crown development of each tree, a feature which is determined 

 largely by the density of the stand. Moreover, it is to be taken for 

 granted that, other things being equal, the yield will increase with 

 age until a certain age limit is reached. An exact study of the 

 factors influencing both germination and yield is much more com- 

 plicated than one in which germination alone is considered. Since 

 this study was undertaken with the primary object of determining 

 the conditions affecting germination, the data on yield are incom- 

 plete; nevertheless it is worth while to make a few comparisons based 

 upon the data available, making due allowance for the evident inac- 

 curacies in the results. 



[Cir. 196] 



