444 EXPERIMENT STATION RECOED. 



attributed largely to the failure to recognize soil acidity as a fundamental 

 requirement of these plants." 



The author found that the root-system of the swamp blueberry is devoid of 

 root hairs by means of which ordinary agricultural plants absorb their moisture 

 and food. The rootlets of healthy plants of the swamp blueberry are inhabited 

 by an endotrophic mycorrhiza which appears to have a beneficial effect upon 

 the plant. The acid peaty soils in which the swamp blueberry thrives contain 

 large amounts of nonavailable nitrogen, but are deficient in available nitrogen, 

 owing to the inability of the nitrifying bacteria to thrive in such a soil because 

 of its acidity. From the evidence at hand the inference is drawn that the 

 mycorrhizal fungus transforms the nonavailable nitrogen of such soils into 

 nitrogen available for the nourishment of the plant. Furthermore, in accord- 

 ance with the work of Miss Charlotte Ternetz with mycorrhizal fungi of certain 

 related European plants (E. S. R., 19, p. 425), it is suggested that the mycor- 

 rhizal fungus of the swamp blueberry may transform the free nitrogen of the 

 atmosphere into a form of nitrogen suited to the use of the blueberry plant. 



The principal features of successful pot culture are the autumn germination 

 of the seeds, the use of suitable acid soils, plunging the pots in sand to control 

 conditions of moisture and aeration, partial shading of plants during the heat 

 of summer, thereby prolonging the active growing season, and exposing dormant 

 plants to outdoor conditions to facilitate normal growth in the spring. When 

 grown in acid soils the swamp blueberry is little subject to fungus diseases or 

 insect pests. 



Based upon experiments already made, 2 methods of experimenting with the 

 field culture of the swamp blueberry are suggested. 



Dimorphic branches in tropical crop plants: Cotton, coffee, cacao, the 

 Central American rubber tree, and the banana, O. F. Cook (U. S. Dept. 

 Agr., Bur. riant Indus. Bui. 19S, i)p. 6-'t, pls. 7, figs. 9).— A study of the branching 

 systems of cotton, coffee, cacao, the Central American rubber tree (Castilla), 

 and the banana leads the author to conclude that these have been specialized 

 on independent lines that can hardly be described on the basis of the usual 

 classification of branches into the 2 general classes of axillary and adventitious. 

 " Each normal plant produces 2 kinds of branches with regular differences of 

 form and function." 



This bulletin contains general considerations relative to the structural sig- 

 nificance of dimorphic branches, their similarity to alternating generations, 

 and different types of dimorphic branches, describes the nature and extent of 

 branch dimoiTohism in each of the above named crop plants, and points out 

 numerous cultural applications of these specialized habits of growth, including 

 the relations of dimorphic branches to acclimatization and to weevil resist- 

 ance in cotton plants, to the methods of propagating and pruning of rubber 

 trees and coffee trees, to the habits of growth and the pruning of cacao, and to 

 the propagation of the banana. 



The banana plant produces 2 forms of suckers or offshoots corresponding to 

 the dimorphic branches of the woody species. -These are the so-called sword 

 suckers which represent true permanent branches of the rhizome and the so- 

 called broad-leaved suckers which arise as relatively small shoots from near 

 the surface of the ground. Although the sword suckers are generally used for 

 propagating purposes, an experiment conducted by H. Pittier in Costa Rica has 

 shown that dormant tuber-like suckers of the broad-leaved type which are 

 formed on uprooted rhizomes constitute a readily portable form of propagating 



'^The possible value of this acid condition was suggested but not followed up 

 in the blueberry work at the Rhode Island Station (E. S. R., 15, p. 42). 



