BEHAVIOR OF SPECIES OF CACTI. 21 



applies more especially to the larger species, mainly of Mexican 

 origin, but also to a«great number of the larger forms of the south- 

 western United States. 



When grown from cuttings the average species will produce fruit 

 the third year, and the larger forms will continue to increase in 

 size, generally forming a bush of more or less hemispherical outline, 

 unless pruning is practiced, thereby shaping them artificially into 

 trees. When grown from seed, however, all of these larger species, 

 both spineless and spiny, are arborescent in habit, producing an erect, 

 cylindrical trunk of greater or less dimensions and then expanding 

 int > a top, like any other tree. This point is beautifully illustrated 

 in Plates VI, figure 2, and VII, figure 2, where are shown two plants 

 of the Mexican durasnillo, 1 one grown from a cutting and the other 

 from seed. Plate VIII, figure 1, shows another arborescent species 

 about 2| years old, from seed. The peculiarities mentioned are 

 clearly shown in these illustrations. The point will be still more 

 clearly appreciated if one stops to consider what a different form of 

 plant would result if the third joint from the ground (PL VI, fig. 2) 

 were to be planted. In that case, if the cutting were inserted to its 

 middle in the ground there would result a bush, branching from its 

 very base, with the main branches ascending and the resulting plant 

 a hemispherical shrub ; in other words, an opuntia tree grown from a 

 joint is headed on the ground. 



This is the condition of practically all plants in cultivation in 

 conservatories and gardens, as well as in a great many of those 

 growing naturally in their native countries, for even there the re- 

 production is largely vegetative, resulting in possibly the majority 

 of cases from chance cuttings. 



This has both an economic and a scientific bearing, economic in 

 that the habit of the plants is an important consideration when 

 these are to be grown under field culture ; indeed, one serious objec- 

 tion to the plants is that the straggling branches get in the way of 

 the tillage implements and are broken off, resulting in loss and ren- 

 dering the fields unsightly. The best plant for cultivation is one 

 with ascending arms forming a dense, compact head. On the other 

 hand, the systematic botanist is leading his audience far astray when, 

 as is too often the case, he describes the habit of the vegetatively re- 

 produced plant, even though this may be the form commonly seen. 

 In many cases it is next to impossible to-day, without growing seed- 

 lings, to describe accurately the form which the typical plant has — 

 manifestly an impossible undertaking in the vast majority of in- 

 stances. This has led to much of the confusion found in the litera- 

 ture of these plants and contributes not a little to the difficulty of 



1 Opuntia leucotricha. 



