BIOLOGY AND LIFE HISTORY. 



17 



infrequently on mesquite and very commonly on hackberry. The 

 cortical haustoria have persisted for years, in many cases producing 

 an unsightly deformity of the branch or trunk (fig. 7). There is an 

 obvious similarity between this behavior of mistletoe and that of cer- 

 tain noxious weeds, such as Johnson grass, where from an original 

 plant underground rootstocks spread in all directions, sending down 

 more roots into the soil and sending up plant after plant into the air 

 until a wide area is beset by it; also in the further respect that merely 

 cutting off the tops only serves to stimulate the underground parts to 

 greater activity in spreading and breaking out in new places. 



Ftg. 5.— Mistletoe on a branch of a cedar elm tree, showing the starved end of the branch and how 

 mistletoe comes to be terminal on a branch. 



RATE OF GROWTH. 



During the period in which the parasite is becoming established 

 the rate of development, as already shown, is extremely slow. Dur- 

 ing the whole of the first season the mistletoe plant -may not grow 

 more than a quarter or half inch in length. After becoming thor- 

 oughly established, however, growth is relatively rapid, depending. 

 as does the host also, upon the character of the season. The shoots 

 from adventitious buds have been observed to grow to the length of 

 4 to 6 inches in a single season following the spring pruning of the 

 previously developed crop of shoots. In the case of water oaks 

 growing in wet bottom-land soil, bunches of mistletoe have been 

 observed to develop in six to eight years into a shrub having a 

 12579— Bui. 166—10 3 



