﻿4 BULLETIN 9, U. S. DEPARTMENT OF AGRICULTURE. 



FORMS. 



With so many and so varied species there can be no form and no 

 rate of growth common to the whole genus. Some acacias are mere 

 herbaceous plants; others are towering trees; most are shrubs, and 

 some, in fact, are vines or climbers. In certain instances the same 

 plant which has a creeping habit when exposed to cold salt winds 

 on the seashore will be able, a little farther inland, to assume an erect 

 form and, where still better protected, to become a fully developed 

 tall tree. One authority describes these size variations thus : 



Some tiny species hardly exceed 3 or 4 inches in height, and may be crushed like 

 the grass of the field. Most of them are shrubs, or trees of moderate size, while at 

 least two species attain the stature of large forest trees, both of them being found to 

 measure up to nearly 4 feet in diameter, while one has been found to attain a height 

 of over 100 feet, and the other the extraordinary height of 150 feet. 1 



The largest acacia is probably Acacia bakeri, of which specimens 

 have been described as over 160 feet high, with a clear length of from 

 50 to 60 feet and diameters of from 2 to 4 feet. Other large trees are- 

 Acacia melanoxylon, A. longifolia, A. dealbata, and A. decurrens, all of 

 which may attain a height of 100 feet or more. A. salicina, A. excelsa, 

 A. elata, A. prominens, A. pendula, and A. binervata are also large 

 trees, ranging from 30 to 80 feet in height. 



Those which are most used for commercial products, and par- 

 ticularly for tannin, do not need to attain large size or great age 

 before the products are merchantable. Thus they can be managed 

 on a shorter rotation than most forest trees. 



ENEMIES. 



Insects. 



The acacias first planted in California grew so fast, bloomed so 

 soon and so freely, and were so free from disease that most horti- 

 culturists felt sure that acacias would become the most important 

 shade trees for California. This enthusiasm was particularly marked 

 from 1870 to 1876. It was like the subsequent fad in the Middle 

 West for the hardy catalpa or the more recent furore over eucalypts 

 in California. There followed, however, a sharp reaction because 

 of the ravages of various scale insects, and many trees were cut down. 

 But after the introduction of the vedalia, which destroyed the cottony 

 cushion scale, and the adoption of the various sprays it was found 

 that the acacias are not peculiarly subject to injury by scale insects, 

 and are no more often a haven for the pests than are o^ks, olives, 

 and various orchard trees. The most dangerous insect enemy, 



1 J. H. Maiden, "Wattles and Wattle Barks," Government Printer, Sydney, New South Wales. 



2 For information on insects and methods for their control the reader should apply to the State Experi- 

 ment Station, Berkeley, Cal., or to the Bureau of Entomology, United States Department of Agriculture, 

 Washington, D. C. 



