28 HORTICULTURAL SOCIETY OF NEW YORK. 



while half a mile or so inland it becomes level. On this level 

 portion the injury from cold was very severe, but on the slop- 

 ing portion it was entirely wanting except where obstacles inter- 

 vened to hold back the cold air. So, for example, one rather 

 steep slope showed no signs of injury whatever, except near 

 the base, where a close stone wall about five feet high held back 

 the cold air, acting as a dam and forming, as it were, a little 

 pond. The plants standing in this pond of cold air were seri- 

 ously injured. That the general lack of injur}' was not due to 

 the proximity of the bay is shown by the fact that at the Sub- 

 tropical Laboratory and Garden, right by the water, but level 

 and with the outflow of cold air hindered by a fence and trees, 

 the injury was exceedingly severe. 



To summarize : air drainage is an important factor in the 

 acclimatization of plants in those regions where the general mass 

 of air is not cold but the cold occurs in a rather shallow layer 

 of air. Under such conditions with proper drainage the cold 

 air flows ofif, preventing injury. 



The President — Miami is an extremely interesting place for a study 

 of this kind, and I think there is real value in the paper that has been 

 presented. Does any one wish to make any remarks upon it? 



Dr. MacDougal — This is an interesting paper. Dr. Bessey brings 

 to mind some very accurate experiments made in the same place some 

 fourteen or fifteen years ago by Dr. Roberts at the time of the great 

 destruction of citrus fruits. These experiments were published in 1893. 

 This is a subject that I have been interested in and have published a 

 little on, the last being in 1899, in which I find this inversion of tempera- 

 ture a very important factor in the distribution of wild plants. I find 

 it reaches its greatest accentuation in regions of low humidity and not 

 in arid regions. I have published some observations in a valley where it 

 drains from a mountain range 13,000 feet high. Now, a thermograph at 

 this place, and the observations and the result show the minimum record 

 at times often varies as much as fifteen or twenty degrees, so it may be 

 twenty degrees .below freezing and up on the hill a few hundred feet 

 above, it may be twenty degrees warmer. Now, these inversions of tem- 

 perature have the effect of carrying the distribution of wild plants south- 

 ward, that is to say, downward, down the mountain slopes, in these ravines 

 where the air is cold at night and the plant runs down where it makes 

 existence possible there. This air drainage is accountable for a great 

 many so-called anomalies. That is, jou may have a plant which belongs 

 on the top of a mountain, and find it down some ravine where the cold 

 air flows. 



