RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 



be given for the formaldehyde to evaporate entirely. This will 

 doubtless occur before the soil is perfectly dry. 



When germination is fairly complete, the seedlings well established 

 so as to reach all parts of the soil, and the tendency to succumb bo 

 damping off, if any, outgrown, the surfaces of the puns are sealed 

 over by pouring on the top of the soil, previously Leveled, about 50 

 grams of a melted mixture of paraffin and petrolatum (veterinary 

 vaseline is one of the least expensive forms) in the proportion of 2:1. 

 This congeals at 40° C. and may be applied at 50° C. without anj 

 injury to the stems of the seedlings. Not infrequently, if the XN ilting 

 process requires many days, the seal will draw away from the edgi 

 of the pan, but this is easily rectified by the use of a blunt, smooth 

 stick. At any rate, it is not essential absolutely to prevent direct 

 evaporation from the soil, though a more even distribution of moisture 

 may be expected if such loss is kept at a minimum. 



The weight of paraffin added is determined by weighing the beaker 

 from which it is poured before and after each application. This 

 makes a further addition to the tare. The soil should be fairly moist 

 when the paraffin is applied, so that the latter will not penetrate. 



With coniferous seedlings, provided a good stand has been secured, 

 the withdrawal of moisture and the sealing of the pans may usually 

 be undertaken at four to six weeks after sowing; though in the case 

 of spruce and perhaps other species which root rather slowly a slightly 

 longer period maybe desirable. As has been pointed out, the diflieultv 

 of detecting wilting increases as the seedlings become older and more 

 completely lignified. It is also unmistakably true that the older 

 the seedling the more difficult it is to kill. This is probably due in 

 part to greater resistance to drying out and in part to deeper or more 

 extensive rooting, which would be an advantage if the moistuTe at, 

 say, the bottom of the pan, were not being drawn on as freely as 

 that near the surface. However, observations on the wilting oi seed- 

 lings under direct insolation point unmistakably to resistance 

 creasing with age. When the surface of the soil becomes extremely 

 warm, even if there is an abundance of moisture within reach oi 

 roots, wilting is likely to be evidenced by collapse oi the stem at 

 ground line. The phenomenon is almost identical when the 

 face of the soil becomes dry in advance of the deeper soil. I he se 

 ling is undoubtedly vulnerable to water loss and critical injury 

 the lower part of the stem. Under such conditions ,t is noted tha 

 the younger seedlings usually succumb first, and those which survive 

 one exposure are killed by a repetition which is still more se. . 



It is evident, therefore, that age of seedlings will have an ... poi - 

 ant influence on the results, though this will not be so important 



