40 THE FRUIT OF OPUNTIA FULGIDA. 



soil, sends down adventitious roots of its own which soon become an impor- 

 tant part of the root-sjstem of the new plant. 



From what has been said of the slow development of plantlets from 

 sprouting fruits in the laboratory, it is evident that it takes a number of 

 years to develop a mature flowering plant from a fruit. It is doubtful 

 whether such a plant can mature more than a year or two sooner than a seed- 

 ling started at the same time. 



Examination of plantlets, from sprouted fruits and also of those from 

 fallen joints, shows that not all of the fallen fruit or joint enters into the 

 make-up of the first or basal joint of the new plant. The portion which does 

 so probably depends in part upon the position in which the fruit falls, or is 

 planted, on the soil and on the relative positions on the fruit of the areoles 

 forming the roots and those forming the shoots. It is a common occurrence 

 for a part (often a fourth or a third) of the fruit, including both cortex and 

 vascular bundles, to be cut off by a layer of cork from the part going into 

 the first joint of the new plant (fig. 99). The phellogen from which this 

 cork arises is formed by the parenchyma of the cortical and medullary- 

 tissues. 



The fate of the different parts of the vascular system of the parent fruit 

 has not been followed out in all details, but it is clear that much of the old 

 system plays no important part in the new plant and that some of it is cast 

 off with the cut-off portion of the fruit (fig. 99). The chief part of the old 

 system to do service in the new.plantlet is that which lies most directly 

 between the point of origin of the adventitious roots and that of the primary 

 shoot of the plantlet (fig. 99). These strands quickly become thickened to 

 many times the diameter of the other bundles of the parent fruit. The seeds 

 present in these sprouting fruits evidently persist indefinitely in the flesh of 

 the latter. Their ultimate fate has not yet been determined, as the oldest 

 plantlets seen which were known to be of this origin were but 2 years old. 



While roots may arise from parts of the fallen fruit outside the areole, 

 such as the scar of the fruit-stalk or of the perianth, it is apparently not pos- 

 sible for shoots to arise elsewhere than from the areole. The experiment 

 was tried repeatedly of planting fruits, all the areoles of which had been 

 destroyed by cauterization, to determine whether other superficial tissues 

 might be stimulated to produce new-shoot growing-points. Though some of 

 these cauterized fruits took root in the soil and remained plump and green 

 for 24 months, they developed no visible rudiment of a shoot. 



An attempt was made also to determine whether halves or quarters of a 

 fruit, in which the cut surfaces were either covered with vaseline or dried, 

 could be made to take root and form new shoots. This was partially success- 

 ful in only a few instances where part of the piece remained green for a time 

 and some roots were formed, but in no case was a single shoot formed. This 

 was due apparently to the fact that a softening and decay of the exposed pulp 

 of the cut fruit took place, similar to that which occurred in fruits punc- 

 tured for the insertion of cut seeds (see p. 33). 



