tit JUL 



^"bl If v ^>\a^ 



^ < Established 1884. 



I 1 

 Vol. XIX The West American Scientist No. 1 



. 



JULY, 1915 ♦ 



SI 



PLANT ADAPTABILITY 



A curious instance of how a plant may adapt itself to un- 

 usual conditions was observed in an individual Button Cac- 

 tus, recently found by the writer in Texas. 



Mammillaria micromeris is a small growing cactus usually 

 found on bare ground or in rock crevices on the summit of 

 limestone hills, where they are exposed to the sun. Com- 

 monly (as found by the writer) the plant is simple, with 

 a depressed top, slightly' elevated above the surrounding 

 soil or rock-surface. In Mexico it more frequently occurs in 

 cespitose masses, but in Texas, its northern limit of distri- 

 bution, it more often resembles a small white button lying 

 on the ground, whence its popular name. 



In ascending one of the steep hillsides leading to the flat- 

 tened top of the limestone formation frequented by this 

 cactus, I chanced to find a dead plant of the lecheguilla 

 (Agave lecheguilla), and above its cluster of dried leaves was 

 a head of the button cactus, facing the sun. Digging down 

 I finally secured the remarkable specimen described as fol- 

 lows : — greatest diameter, near the summit, 35 mm ; least 

 diameter 8 mm, near the base ; hight of stem, 11 cm ; length 

 of the elongated slender portion of the stem between the 

 base and the normal top, 9 cm ; greatest diameter below the 

 normal top, 25 mm; this prolongation, by which the plant 

 raised itself from the shade of the lecheguilla was too weak 

 to support the plant, and was covered with scanty clusters 

 of weak slender spines. 



Evidently the plant exerted all its energy in forcing an 

 upward growth to the light, and when it had reached the 

 sunshine it was unusually well prepared to stand the strug- 

 gle for existence, with roots strongly entrenched in the 

 shade, and with a greater storage capacity because of its 

 elongated trunk, was able to grow rapidly to a size greater 

 than its neighbors under normal conditions. 



A smaller similar specimen was also found, which had 

 developed a stem sufficiently strong for the support of its 

 well-developed head. 



MOLLUSCAN WORLD 



BINNEYA NOTABILIS 



Shell light, thin, ear-shaped, horn-colored, 7 to 14 mm 



1 



