THE FRUIT OF OPUNTIA FULGIDA. 39 



of them 5 cm. long, 1 mm. thick, and often branched several times. These 

 roots arise chiefly on the buried portion of the fruits and always develop 

 from an areole, from the broken surface of the fruit-stalk, or more rarely 

 from near the edge of the perianth-scar. From this statement it will be 

 seen that roots may arise at either the basal or apical end of the fruit, or 

 at both, depending on whether the fruit is laid horizontally or whether one 

 end is placed lower in the soil. My observations do not confirm the con- 

 clusion of Tourney (1905) that the " roots appear chiefly at the basal end of 

 the fallen joint." Though the roots arise from the areole, they do not arise 

 from its growing-point, in the middle of the areole, but from the still active 

 tissue around its edge. Very often a root pushes out above the cluster of 

 bristles on the adaxial mara-in of the areole, but a root mav rise also from 

 any other part of the margin (fig. 100). One or several roots may arise 

 from the same areole. When a root is developed from the scar of the fruit- 

 stalk it is usually from its margin. As such a root matures, however, the 

 vascular bundles of the root soon come to form continuations of the bundles 

 at the base of the fruit. When a root develops on a perianth-scar it appears 

 always to originate in the region of the cork cambium, and it breaks through 

 the cork itself in emerging (figs. 78, 99, 100). 



The initiation of a shoot bv a detached fruit does not occur imtil some 

 time after the first roots are developed on it. The formation and function- 

 ing of roots are apparently necessary antecedents to shoot formation. In 

 fruits planted in the greenhouse at Tucson on April 26, kept well watered 

 and at rather high temperatures, shoots began to push out of some areoles by 

 May 25, and on the following September 10 all but one or two of the 18 

 fruits planted had one or more vegetative joints on it. Some of the latter 

 were 2 cm. long. Similar results, though not so universally successful, were 

 obtained from plantings at South Harpswell and Baltimore. One lot of 

 fruits planted at Baltimore produced shoots only 3 or 4 cm. long in a year ; 

 while others, with more soil, had shoots 10 cm. long in five months. 



One or several joints may arise from each fruit, either simultaneously or 

 successively. They may arise from areoles on the exposed surface of the 

 planted fruit or sometimes from those joints at the surface of the soil, but 

 nearly always from the larger areoles of the apical half of the fruit. This is 

 without regard to whether the fruit is planted on the side, with apex down, 

 or with the base dowm. 



The shoot arising from the areole of a fallen fruit is formed by the grow- 

 ing-point of the areole, just as a flower is, or just as a branch is from a vege- 

 tative joint. The new shoot, however, is for a long time different from the 

 branch of a mature plant in remaining slender and in the permanent delicacy 

 of its spines (fig. 78). In fact, it has the appearance of one of the early 

 joints of a seedling. The primary shoot, as developed in the greenhouse in 

 Baltimore, usually does not branch until the second season. Quite early in 

 its development the new shoots, especially if it has arisen near or under the 



