82 MISSOURI BOTANICAL GARDEN. 



from 8 pea to that of a walnut (pi. 8) . Specimens of the large 



size were always associated with large stems. Those found on 

 stems three years old had attained a mass 1 to 1.5 cm. in 

 diameter. The cluster is usually very compact and resembles 

 somewhat that of the alder and Elaeagnus, although differ- 

 ing in this respect from Ceanothus. Harshberger claims that 

 the tubercles are of very slow growth and tries to determine 

 the age of a cluster by comparing it with the age of the plant 

 on which it is found, but his estimate can be only relative. 

 The masses shown in the photograph (pi. 8), growing on 

 plants three years old, have attained 2 cm. in diameter. Ac- 

 cording to his statement some plants were twenty years old. 

 Granting that growth be uniform, and if three years' growth 

 will produce a mass 2 cm. in diameter, on a plant twenty 

 years old, one would expect a cluster a half a foot in diame- 

 ter, a size not attained on any plant observed by either 

 Harshberger or myself. 



The individual tubercle may be described as a short 

 thickened rootlike structure which branches di- or trichoto- 

 mously after having attained a certain length. The longest 

 individual branches found were 2 mm. in length. Their 

 thickness varies from .5 to 1 mm., the older portions, how- 

 ever, being the thickest. One peculiarity of these tubercles 

 is that, after having attained a certain length, their tips grow 

 out into a narrow thread-like structure, often attaining 1.5 

 to 3 cm. in length (f. 28). This again sends out lateral 

 branches which may be found entwined amongst the roots 

 and grass blades. In vigorous growing material the out- 

 growths of this kind appear quite like ordinary roots of the 

 plant except that their shape is more tapering toward the tip. 

 The structure of the tubercle will be described in detail in 

 a subsequent paragraph. 



The color of the youngest tubercles is a light gray to pink 

 changing to a flesh color with age. The long slender tips, 

 nearly colorless when young, become brown as they dry, 

 through exposure to the air and soil. The very old and dry 

 tubercles are dark brown or even black, a color which was 

 attributed to them by Harshberger, who made his investi- 

 gation with dried material only. 



