292 IOWA ACADExMY OF SCIENCE Vol. XXV, 1918 



witli increase between extremes. Thus if 'he temperature is 

 eon.stant at 60^ F. on one day and varies t'rom 50° to 70^ F. 

 with a mean of 60° on another, g-ermination is his'hest following 

 the latter. 



The practice in testing- seed in greenhouses is to hold air tem- 

 peratnre to a minimum of 50° F. An examination of thermo- 

 " graph sheets and germination records indicates that minimum 

 air temperatures down to 32° F., the freezing point, do not 

 retard germination and in fact appear to accelerate it unless 

 they are prolonged. Seed in the nurseries is of course sub- 

 jected to a wider variation in temperature than in the green- 

 house, but it is diilPicult to say that this result's in slower germi- 

 nation. It is probable, though not proved, that the accumulated 

 temperatures above 40° F. control germination. The author dis- 

 cusses the vitality of seeds of the three conifers. He finds that 

 in the case of Jeffrey pine, seed several years old may be used. 

 In case of yellow pine the germination percentage falls off 

 after two years. Seeds of incense cedar fall to 33 per cent the 

 second year, and have practically no germination after the 

 tliii'd year. Three years tests on over forty lots of seed of 

 sugar pine gave no consistent or reliable results. The author 

 finds it important to know the average rapidity of germination 

 so that enough young plants be produced before the necessiry 

 time for transplanting. 



He finds in his tests that northern seed is more rapid and shows 

 h\ss variation than southern seed. He believes that for planting 

 the percentage of effective germination should be determined 

 for each species; as for instance, he has found it in the case of 

 yellow and Jeffrey pines to be about 50. 



Clifford* discusses germination distributed over a period of 

 time; as in wliite pine, some grow the first year, many the .sec- 

 ond year, a few the third year. With regard to geograi)hical 

 conditions; the farther north and the higher the altitude, the 

 smaller the seed and the smaller the percentage of germination, 

 altliough the quantity produced is often immense. The author 

 quotes from Rafn determination of germination percentage of 

 many species, which indicate how variable is the value of seeds 

 on the market. 



Of the general statements which we find the following may 

 serve the purpose of this paper. Jolui Nisbet'' quotes from Ney 



'Gifford, J.. Practical Fcre.stry, pp. li)2. 106, 111. 112. 



^I^ritish Forest Trees and Their t-"il\itultural Characteri.''tics and Treat- 

 ment, 48. 



