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a, Vertical and, b, horizontal extensions of root-system of Opuntia versicolor, Tumamoc 

 Hill, views of which are shown in plates 10 and 11. One-fortieth natural size. The root-area 

 of the cactus contained other perennials of which one specimen of Echinocactus wislizeni, at the 

 base of the cactus studied, is shown in yellow, one specimen of Jatropha cardiophylla in purple, 

 and the tips of the roots of a neighboring Opuntia discata, on margin of plate, are in yellow. 



