ECOLOGY OF WOODLAND PLANTS. 945 
the moist Coal-Measure Oak woods in the West Riding of 
Yorkshire, and forms what we may call a complementary 
association; the subaerial parts, as we have seen, are edaphically 
complementary, the aerial parts being seasonally complementary. 
Maedougal (62) recently made a study of temperatures at 
different depths, with the view of showing the extremes to which 
the different parts of plants are subjected, and found a consider- 
able range. He records that in New York during the months 
of October, November, and December, 1902, the ground was at 
times frozen at a depth of one foot. Mr. Charles Brook has 
kindly supplied me with readings for a corresponding period 
taken by him at Harewood Lodge, Meltham, which will serve to 
indicate the variations in this district. Rarely is the ground 
frozen here to a depth of a foot, but this, however, did occur 
in February 1895, when the ground was frozen to a depth of 
20 inches for 13 days. Probably not since 1809 has so low a 
temperature been recorded here. Maximum temperatures on 
the grass were not taken, but I give the maximum and minimum 
at 4 feet above the grass. 
The relatively slight variations seen to occur at one foot, and 
still less at two feet, below the surface will obviously be an 
advantage to deep-rooted plants, especially to those vegetating 
early in the year. In this connection it is interesting to note 
that of the three plants of this association, the first to make 
its appearance (Scilla festalis), and therefore most likely to be 
injured by early frosts on account of its early vegetative growth 
and flowering, is the one most deeply rooted and also, as we shall 
see, possesses for all practical purposes an unfreezable sap. 
Temperatures (° F.) recorded at Harewood Lodge, Meltham. 
Altitude 510 feet. 
Absolute monthly maximum and minimum temperatures 
at 4 feet above the grass. 
1902. 1903. 
June. July. Aug. Sept. Oct. Nov. Dec. | Jan. Feb. Mar. Apr. May. 
79:2 76:3 700 735 609 549 548 | 51-7 549 620 587 75-9 Max. 
390 874 387 342 330 279 164 | 180 298 305 266 320 Min. 
469 289 813 593 279 270 384 | 33-7 251 3815 321 43-9 Diff 
Absolute minimum temperatures recorded on the grass. 
Maximum temperatures not taken. 
270 323 3250 289 27:5 201 141 | 160 287 230 187 270 
