[Reprinted from TORREYA, Vol. 13, No. 6, June, 1913.] 



A CASE OF ABNORMAL DEVELOPMENT OF A SHORT 

 GROWTH IN PINUS EXCELSA 



BY ARTHUR H. GRAVES 



The characteristic development in the genus Pinus of two 

 sorts of shoot axes long and short is well known to all who are 

 acquainted with the genus. The long growth (Langtrieb) is 

 represented by the main axis or axes of the shoot system; the 

 short growths (Kurztriebe) consist of much abbreviated branches 

 which are borne on the long growth, arranged spirally upon it, 

 and subtended by its scale-like leaves. These short growths 

 or branches are characterized primarily by the fascicles of 

 leaves they bear; each one, in the group of the white pines, 

 developing normally five leaves, in a whorl-like cluster or "fas- 

 cicle." Microscopical examination shows near the base of these 

 leaves, and surrounded by them, a tiny growing point at the 

 terminus of the short growth. Under ordinary conditions this 

 growing point never develops further; and at the end of two or 

 two and one half years the whole short growth is shed, in essen- 

 tially the same manner as a leaf is cast from one of our deciduous 

 trees. 



Under special conditions, however, as for example when the 

 growing point of the long growth is injured, a development of a 

 short growth into a long growth rarely occurs.* An interesting 

 case of this kind was recently found by the writer on a tree about 

 15 years old of Pinus excelsa Wall, in the New York Botanical 

 Garden, and is illustrated in figure I. The five leaves com- 

 posing the original fascicle may be seen at the base of the 

 shoot, one of them having been slightly twisted in order to show 



* Engler, A., und K. Prantl. Die natiirlichen Pflanzenfamilien nebst ihren 

 Gattungen und wichtigeren Arten insbesondere den Nutzpflanzen. 2 1 : 29 note. 

 Leipzig. 1889. 



