18 BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 



976, from the branch 321. On very old brooms of the western larch 

 it is often noticed that the needles begin to turn yellow some time 

 before those on the branches of uninfected trees. Exactly the re- 

 verse may occur in the case of recently formed brooms, owing to 

 the larger amount of newly stored food materials in the swelling 

 on the main branch and the branches of the brooms. That the 

 broom may be the cause of a great localization of food substances 

 is indicated by the fact that in heavily infected Douglas fir and 

 larch the last part of the tree to succumb is usually the smaller and 

 younger brooms of the tree. Frequently trees of these species are 

 noticed with only a single small broom living, the rest of the branches 

 being apparently dead; likewise the old and exhausted brooms. The 

 increase in the number of needles on the broom due to the multi- 

 plication of its branches is usually at the expense of the needle de- 

 velopment on the normal parts of the tree. For this reason an 

 excess of food materials for the tree as a whole does not take place. 

 The foliage beyond the broom becomes thin and, in most cases, 

 the end of the branch dies (figs. 12 and 14). The food materials 

 are entirely stored and appropriated by the broom itself. The 

 phenomenon is analogous to the formation of spiketop of the main 

 trunk. 



That brooms do not always necessarily mean an increase in foliar 

 surface for the host, since we have seen that parts of the branches 

 not supporting brooms frequently die, is shown by a comparison of 

 the needles of old brooms with those of normal branches either of 

 the same tree or of uninfected trees. Such a study was made in the 

 case of the Douglas fir. It was found that the needles of the brooms 

 on the trees studied were uniformly a little less than one-half as long 

 as the leaves of the normal branches (PI. IV, fig. 1). Neither were 

 they as thick or as broad. By compensation it would be possible to 

 determine approximately the actual foliar surface of a given broom 

 and compare it with that of a given normal branch of the same 

 whorl and of the same age. This difference in the size of the needles 

 was found to hold good only in the case of old, mature brooms of trees 

 which were beginning to be suppressed. Young brooms, especially 

 on young trees from 10 to 20 years old, often have abnormally long 

 needles on the still upright branches, but this condition is not long 

 maintained. Soon these branches begin to droop, the broom be- 

 comes denser, the needles disappear from the center outward, and 

 they are often sparingly distributed along the stems but more densely 

 assembled on the last few years' growth (fig. 13). With continued 

 suppression of the Douglas fir and exhaustion of the broom, a new 

 type of branching often appears. The long trailing, weeping-willow- 

 like branches cease to elongate and the cortical stroma of the parasite 

 is enabled to catch up with the terminal bud and kill it. The branch 



