168 PROCEEDINGS OF THE ACADEMY OP [1894. 



the tree are abundant. Some of these are among the fallen ones, 

 but few, apparently, in proportion to those from among the last 

 season's growth. There is no fixed order in the dropping of the 

 leaves. On a branch with say ten last year's leaves, it may be the 

 first, fourth or fifth in the order of growth, or it may be a few of the 

 later ones. In some cases all of the last year's growth will fall 

 from the branch, leaving a few healthy leaves below of the year 

 previous to the last. These will probably fall in a natural manner 

 later in the season. 



Just here arises the question: What is the "natural manner" of 

 the fall of the leaf? If a branch of any tree be broken off before 

 maturity, the leaves dry, but remain attached to the parent branch. 

 There is no "fall of the leaf" in this case. On the same branch, 

 if it had been left on the parent stem, the leaf would have formed 

 cork cells at the junction of petiole and stem, and have fallen by mere 

 disarticulation at that point, in due season. Histology has taught 

 us that cork cells are differentiated from other tissue, but the man- 

 ner in which this has been brought about has not been demonstrated 

 so far as the writer is aware. It has been thought that the following 

 observations in connection with this subject may at least direct 

 thought, if they throw little direct light on the subject. 



On the leaves of the holly which are to fall, one or more small, 

 black blotches underneath the epiderm appear here and there, being 

 apparent both on the upper and under surface of these leaves. At 

 this season the parenchyma takes on a yellow cast, the black 

 blotches, however, retaining their character. Disarticulation then 

 follows. The leaves which are perfectly green, and with no dark 

 blotches on them, continue on the stem. The connection between 

 these blotches and the fall of the leaf is undoubted, and we may 

 almost as logically say they are connected with the formation of the 

 cork cells which act directly in disarticulation. 



Those of us who have had a wide experience with living vegetation 

 have no difficulty in surmising that these dark blotches are of a 

 fungous character. My good friend, the eminent mycologist, Mr. J. 

 B. Ellis, of Newfield, New Jersey, after a microscopic examination 

 of these fallen leaves, finds evidence that the marks are caused by 

 a minute fungus, though in this and similar instances he has never 

 been able to get nearer the fact than that they are manifestations of 



