U. S. DEPARTMENT OF AGRICULTURE. 



so readily, probably on account of rather poor drainage where it was 

 planted, but there is no apparent difference in the spineless areas 

 produced. This is a rare and peculiar instance of spinelessness which 

 has not, as in other cases, yielded to the process of selection. 



On the central highland of Mexico there occurs a cylindrical-]' ointed 

 low form known to the botanist as Opuntia tunicata. This interest- 

 ing species is of no economic importance except that it is a nuisance 

 wherever it grows, breaking off reproductive joints almost without 

 provocation and thereby rapidly spreading wherever stock is pas- 

 tured. This species, imported by the writer from the region of San 

 Luis Potosi ( PL IV, fig. 1 ) , and another specimen furnished by Mr. 

 Alwin Berger from the collection of Sir Thomas Hanbury at La 

 Mortola, Italy, have behaved in the same way. The La Mortola 

 specimen has been under observation longer, however. It was 

 received in May, 1908, and planted at San Antonio and Browns- 

 ville, Tex. 



The plant at Brownsville has been under observation for prac- 

 tically five growing seasons. It was established from a very long 

 cutting, fully a foot in length and characteristically spiny. This 

 grew readily, but instead of giving rise to other joints of its kind, 

 a very large number of small, subglobular, short, delicately spined 

 joints were produced. (PL IV, fig. 2.) These were almost and 

 often quite without sheaths on their spines. They broke off very 

 readily, and nearly all took root in the well-cultivated ground, soon 

 establishing a patch a foot or more in diameter. The original cutting, 

 however, retained many of these small joints, which have become 

 firmly established, growing to a total height of not over 4 inches 

 in five years. Throughout the first four growing seasons no growth 

 excepting these subglobose joints was made. None of the spines 

 which give character to the plant were in evidence at all. During the 

 fifth year, however, the joints have become a little larger, extend- 

 ing to 2 or 3 inches in length and developing a few much longer 

 spines with silvery white sheaths at their distal ends. These spines 

 are by no means as long as normal for the species but are still quite 

 characteristic. 



In the spring of 1912 some of these small subglobose joints were 

 transferred to Chico, CaL, and have maintained the dwarfed condi- 

 tion the first summer. 



This character of groAvth is not particularly remarkable, except 

 for the long period of five years before the plant begins to assume 

 its adult form. In its natural habitat the reproductive joints are 

 common to both this and other related species, but the normal condi- 

 tion of the plant is assumed in a much shorter space of time. 



Such behavior is particularly important, in that it leads to an 

 uncertainty regarding the identity of different forms and has in 



