PAPERS ON BIOLOGY AND AGRICULTLIRE 85 



NOTE OX JUVENILE LEAVES IN THUJA 



OCCIDENTALIS 



Prof. W. G. Waterman, Northwestern Unrtrsity 



The specimen described was obtained in the course of 

 some experimentation on juvenile leaf production in Thuja 

 occidentalis, suggested by some unpublished work by Doc- 

 tor Land of the University of Chicago. Land reported that 

 he was able to produce juvenile (needle) or adult (scale) 

 leaves by varying the moisture condition of the air sur- 

 rounding the young plants. 



Among the specimens being studied were three plants 

 each about three years old which had been placed in dry 

 conditions. These in some way were overlooked, and when 

 noticed again one was dead, the second nearly so, and on 

 the third about half the branches had died. This third plant 

 was revived simply by furnishing abundant water to the 

 soil in its pot. The dead branches fell off, and new juvenile 

 shoots appeared in many places on the main stem and 

 branches. Fig. 1. 



It is generally known that the seedling of Thuja consists 

 simply of one elongated tuft of rather soft needle leaves. In 

 the second year this elongates and usually one side branch 

 appears and bears scale leaves. These scale leaf branches 

 increase in numbers in succeeding years but for a number 

 of years the end of the main axis bears the needle leaves, 

 until it is finally lost sight of and presumably fails to con- 

 tinue growth after the tree increases in size. It has been 

 noticed that young shoots coming out at the base of the 

 main stem in conditions of strong shade and moisture will 

 usually be of juvenile type. 



In this case, juvenile shoots appeared in great numbers 

 on all parts of the plant and one in particular, shown in 

 Figure 2 has branched, but both branches bear juvenile 

 leaves. In observing the specimens collected for this 

 work, it was noted that there was considerable evidence 

 of individual specificity in the production of juvenile shoots, 

 individuals producing them rather freely, when apparently 

 similar individuals under similar conditions produce only 

 scale shoots. The specimen before its partial desiccation had 



