Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/17

 clump-cured bamboo dipped separately in the same solution and exposed continuously to beetle infestation were still uninfested when this last examination was made.

H. K. Plank and R. Ferrer Delgado

A comparison as regards susceptibility to attack of the bamboo powder-post beetle was completed with culms of 5 different ages of the large-leafed variety, Dendrocalamus strictus Nees, and Bambusa vulgaris Schrad. ex Wendl. The over-all susceptibility of D. strictus was 18.0 percent. As in previous tests, the first-year growth of B. vulgaris tended to be more heavily infested than that of later ages. With D. strictus the tendency was the reverse, in this respect resembling Sinocalamus oldharmi (Munro) McClure. In B. vulgaris there occurred the usual trend for the base of the culms of all ages to be more heavily infested than the middle, and the middle more than the top. However, in the fifth-year culms the middle part was attacked the most. This latter condition also maintained in all ages of D. strictus except the second, but the number of beetle attacks was too small for the differences between parts to be significant within any one age. In B. vulgaris there was also the usual tendency for starch concentration to decrease with age, but in D. strictus it increased in all culms of successive ages except the third. This association of starch concentration with beetle infestation corresponds closely with that previously shown for the same ages of B. vulgaris and S. oldhami.

Unlike other species low in starch, Dendrocalamus strictus showed no correlation, at any of the ages tested, between beetle attack and high moisture content and low specific gravity of the wood. Neither was there any correlation between beetle attack and shrinkage in volume of the wood on drying. In spite of the fact that the fifth-year growth contained less moisture, was heavier, and shrank less on drying than the first-year wood, it was attacked more by the beetle. This inconsistency was no doubt due to uneven distribution of what little starch was present and the consequent irregular variation in small numbers of beetle attacks.

R. H. Freyre and H. E. Warmke

The experiment established last year for comparing the relative forage production and nitrogen fixation of five legume-grass combinations has been carried through four harvests in the south field and three in the rubber field. On the basis of yields to date certain trends are evident. In the south field, grass-legume combinations are producing significantly more forage than either grass or legumes alone. Under the poor conditions of soil and moisture and partial shading which exist in the rubber field, competition between the grass and legumes appears to be reducing total yields in grass-legume combinations. Vigorous and long-lived legumes, such as tropical kudzu