Dec, 1902.] Observations on Self-Pruning. 329 



Euonymus atropurpureiis Jacq. Shed twigs from one to four years old 

 were collected. 



Acer saccharinum L. 



Acer rubrum L. 



Polycodiutn stameneum (L,.) Greene. Self-prunes twigs abundantly. 



Vacciniutn vacillans Kalin. 



The following two grapes were studied and found to prune in 

 the normal way for such plants by the formation of cleavage 

 planes corresponding to leaf nodes in twigs of the season : 



Vitis labrusca L. Wild variety.! 



Vitis bicolor L,e C. 



As stated in the beginning of this paper cleavage planes are 

 often formed to separate the fruit from the parent plant. It is 

 interesting to note some of the ways in which this is accom- 

 plished. In the simplest cases a cleavage plane is formed at the 

 basae of the fruit, which falls off while the peduncle dries and 

 decays awa}-. This is the case in Rhus glabra L,. In others the 

 Separation laj'er is formed at or near the base of the peduncle, as 

 for example in the ground cherr}-, Physalis pruinosa L,. In this 

 herb a very perfect cleavage plane is formed in the peduncle. In 

 the apple and pear the separation of the frtiit from the tree is 

 accomplished in the same wa}^ by the development of a rather 

 imperfect cleavage plane or separation layer. In some plants, as 

 in Primus americana Marsh., or in Benzoin benzoin (ly. ) Coult., 

 the fruit first falls off and afterwards a cleavage plane is formed 

 at the base of the peduncle. In the plum the peduncle sometimes 

 dries off and is not immediately shed, even though the separation 

 laj^er is formed. When the fruit is produced on panicles or 

 cymes there are also several methods of procedure. In the dog- 

 woods, as in Cornus asperifolia Mx., the berries drop off singly, 

 and later the fruiting cyme is closely excised by a smooth cleav- 

 age plane ; while in the smooth sumac, as stated before, the 

 berries drop off in the same way, but the much branched panicle 

 remains to decay gradually. In the chestnut (Castanea dentata 

 (Marsh.) Borkh.), the stems which bear the burs become quite 

 woody, but a cleavage plane is formed and the entire fruiting 

 branch is thus pruned off. 



The writer has had some difficulty in looking up the literature 

 on the subject of self-pruning. This may be because no dis- 

 tinctive term has come into use for this common and most 

 interesting phenomenon of our shrubs and trees. The following 

 is a list of recent American papers bearing upon this subject : 



1885. Trele.'VSE, Wm. When the Leaves Appear and Fall. Second 

 Ann. Rept. Agr. Exp. Sta., Univ. of Wisconsin, for 1884. p. 59. 



1892. FoERSTE, Aug. F. On the Casting-off of the Tips of Branches 

 of Certain Trees. Bull. Torr. Bot. Club, /p.- 267-269. 



