INSULAR EXPERIMENT STATIONS. 25 



is formed. In general no essential difference appears between 

 healthy and sick soils in regard to the number of aerobic bacteria, 

 but a difference is found in the number of anaerobic organisms pres- 

 ent. The investigations thus far carried on have shown that the 

 butyric acid is a product of several kinds of bacteria, the varieties 

 thus far observed in Porto Rico appearing to be facultatively 

 anaerobic. Disinfecting experiments have shown the possibility of 

 correcting the injurious properties of the soil through the destruction 

 of the bacteria, and the application of lime and gypsum to such soils 

 has proved beneficial in some instances. 



The orchards of citrus fruits are coming into bearing, and it will 

 soon be possible to report definitely upon the value of certain varie- 

 ties for Porto Rican conditions. Out of 50 varieties of oranges 30 

 fruited this year, of 16 varieties of grapefruit G fruited, and 8 

 varieties out of 13 of lemons bore fruit this year. The varieties on 

 the station grounds represent all the leading commercial forms, as 

 far as they could be obtained, as well as a number that are less known 

 and a few promising local seedlings that appear of value. Experi- 

 ments are being carried on to determine the best kind of stock for 

 citrus trees in the different types of soils of Porto Rico. The ferti- 

 lizer experiments with citrus trees have been in progress for four 

 years, and it is hoped that with one more year's work it will be pos- 

 sible to formulate some definite conclusions regarding their use. 

 Plantings of mangoes, avocados, and other tropical fruits have been 

 made and attempts are being put forth to propagate the best varieties 

 as rapidly as possible. Some miportant data regarding the inarch- 

 ing of mangoes have been secured and the horticulturist has been 

 able to produce inarched trees ready for setting in the orchard 

 within three months of the time when the seed for the stock was 

 planted 'n pots. The attempts being made to reforest the bare hills 

 and wet grounds of the station are progressing favorably. Various 

 species of P^ucalyptus have been introduced and appear promising 

 for future planting. Considerable time and attention is being paid 

 to the introduction of desirable hf)rticultural species, many varieties 

 being received through the cooperation of the Bureau of Plant In- 

 dustry of this Department. A tract of land has been set aside for 

 the reception of these plants, and the introduction work will be made 

 a definite feature of the horticultural investigations. 



The entomologist has devoted considerable time to studies of the 

 insects affecting citrus trees, and has prei)ared a bulletin regarding 

 these pests, with suggested means for their control. It has been 

 found practicable to fumigate orange and grape-fruit trees in Porto 

 Rico as a means of controlling the scale insects. Some work is also 

 in progress with fungi that are parasitic on scale and other insects. 

 The value of sulphur s])rays and oil emulsions has been tested, and 



