88 MISSOURI BOTANICAL GARDEN. 



inhabits sparingly the gravelly banks of arroyos in the open 

 foothills region just below the steep mountain ascents. 



Attention should be called here to the abnormality in some 

 of the fruits shown in the photograph. Many are affected by 

 a dipterous parasite which deposits its eggs in the young 

 ovary and emerges in the imago stage the following April. In 

 all fruits so injured the areoles, wool, and spicules are enor- 

 mously developed, and in many cases the latter show traces 

 of brown. As stated in a previous publication, the effect of 

 this insect is to turn the young fruit into a vegetative organ, 

 all of the seeds becoming aborted. It remains attached to the 

 plant until the following season, and drops off after the insects 

 have escaped. Engelmann has figured what appears to be 

 this same dipterous larva effect in Pacific Ry. Report, 4, pi. 

 7, f. 3. 185G. 



The type is No. 9619 D. G., collected in the foothills of the 

 Santa Rita Mountains, Arizona, September 23, 1908. The 

 description was drawn in the field beside the plant when the 

 type specimens were collected. — Plates 7; 2, f. 5; 13, f. 6. 



Opuntia congesta sp. nov. 



A low, spreading, very compactly branched, cylindrical-jointed species, 

 4 to 5 dm. high and 9 to 12 dm. in diameter, having such a congestsd habit 

 of growth that there is invariably a great deal of dead stuff in the center; 

 joints variable, 1 to 2 dm. long and 8 to 12 mm. in diameter, tubercular 

 with a low, flat tubercle about 8 mm. long, the upper slope more abrupt 

 than the lower, sharply defined by a slightly but sharply sunken dark 

 green line, which altiiough becoming less distinct is perfectly distinguish- 

 able for two or three years, bright, moderately dark green turning dull and 

 darker to even glaucous and finally scaly, gray-black upon old trunks; leaves 

 3 to 5 mm. long, subulate, mucronate, circular in section, and reddish 

 tinged toward tip; areoles broadly obovate, 3 to 5 mm. long and about 1 

 cm. apart, tawny when young, hut turning through light gray to black in 

 age but having a proliferating tissue in its upper portion which develops 

 new wool even upon three or four-year-old wood, this new growth continu- 

 ing tawny during the current year, often eclipsing the earlier blackened 

 growth, thus elevating the areolar area slightly higher than its original 

 flattened state, often subareolate even when young; spicules yellow in com- 

 pact tuft in upper portion of areole, commonly less than I mm. long, in- 

 creasing slightly but less than 2 mm. and more numerous with age, often 

 scarcely visible until late in the first season; spines normally 1, sometimes 

 2 or even 3, nearly erect, when more than one the lower more or less re- 

 curved and in age in all cases always sloping downward, medium loosely 



