PLANT ORGANS AND ORGANISMS 135 



cerifera, M. Caroliniensis, M. Gale, M. Macfarlanei, and Comptonia 

 asplenifolia. The inciting organism has been isolated by him in 

 pure culture according to Koch's postulates and named Actinomyces 

 Myricarum Youngken. 



The tubercles occur either singly, as is frequently the case on 

 subterranean branches, in small groups the size of a pea, or in larger 

 coralloid loose or compact clusters which frequently attain the size 

 of a black walnut. Each tubercle is a short cylindrical blunt-ended 

 root-like structure which branches di- or trichotomously after attain- 

 ing a certain length. The branches frequently rebranch at their tips 

 which grow out into long thread-like structures from 1-3 cm. in 

 length that may also branch and become entwined about the roots of 

 other plants. The color of the youngest tubercles is a pinkish-gray 

 brown. As the tubercles become older their color changes to brown, 

 dark-brown and even black. (For a detailed description of the 

 Myrica and Comptonia tubercles and their inciting organism, con- 

 sult, "The Comparative Morphology, Taxonomy and Distribution 

 of the Myricaceae of the Eastern United States" by Youngken, in 

 Contributions from the Botanical Laboratory of the University of 



Pennsylvania, vol. iv, no. 2, 1919.) 



> 



THE BUD 



Buds are short young shoots with or without rudimentary leaves 

 (bud scales) compactly arranged upon them. 



The plumule represents the first bud on the initial stem or caulicle. 



Scaly buds are such as have their outer leaf rudiments transformed 

 into scales; there are often coated with a waxy or resinous substance 

 without and a downy lining within, to protect them from sudden 

 changes in climate. Buds of this character are common among 

 shrubs and trees of temperate regions. 



Naked buds are those which are devoid of protective scales. 

 They are common to herbaceous plants. 



Classification of Buds According to Development. i. A leaf bud 

 is a young shortened shoot bearing a number of small leaves. It is 

 capable of elongating into a branch which bears leaves. 



2. A flower bud is a rudimentary shoot bearing one or more 

 concealed and unexpanded young flowers. 



