21 8 Transactions of the Royal Canadian Institute 



between 78 and 80 degrees on four days, at 75 degrees on six days, 70 

 to ']2 on seven days. The rest of the time it never rose to 70 nor fell 

 below 60, save on one day only, August 4th, when it was 59 degrees. 

 For the period July 30th to August 17th, the maximum was 71, the 

 minimum 62, and on four successive days it was exactly 68. The night 

 temperatures ranged between 42 and 54, on 31 out of 70 going below 50. 

 The night growth rates were always very low, the maximum recorded 

 being rather less than 0.4 mm. per hour. 



Humidity: evaporation (fig. 9). — The humidity cycle is similarly 

 regular. The dew point is approached or reached every night. After 

 sunrise the fall in relative humidity proceeds steadily till the 11 hour 

 after which for about four hours it remains fairly steady, usually lowering 

 somewhat. After the 15 or 16 hour it rises again. The course is para- 

 lleled in the evaporation rates, which stand at zero during the night 

 usually until the 7 hour proceeding thereafter to a rate near the maximum 

 at 1 1 hour. The records of several days are here given as examples. A 

 day such as July 8th means a slight movement of air from inland; one 

 such as July 14th that this air movement is not sufficiently deep to keep 

 the cooler air of the ocean from invading the coastal strip of land, at a 

 high altitude and carrying with it the thin edge of the ocean fog bank. 

 Days of low fog are due to the surface invasion of the ocean fog bank, 

 and during such the lower day temperatures occur. Only two such 

 occurred during the period of observation, and, as the parts whose 

 growth was being recorded were near the limit of growth on these days, 

 only low absolute values were obtained and these therefor cannot be 

 used for comparison. 



The total illumination on the plant surface on days during which 

 high fog prevails is little less than otherwise. The fog is frequently so 

 thin that the direct heat of the sun may be felt on the face, and weak 

 shadows are cast. On such days the temperatures are little if at all 

 inferior to those of sunny days. The chiefly variable factor therefor is 

 the light as direct insolation when, on partly foggy days, it may have 

 all the range of values from that through heavy high fog to direct sun- 

 light. 



There is most generally little wind and no rain. During the night 

 "weeping fog" or mist sometimes wets the surface of the ground beneath 

 the trees, and very occasionally may wet the surface generally. 



The plants which afforded the material grew on a gentle slope with 

 southern exposure and were exposed during the whole day to full insola- 

 tion except till about 8 hour, and of course when fog prevailed till the 

 late afternoon, when partial tree shade fell on them, as in the early 

 morning. 



