A SOUTHWESTERN PLANT GROUP. 793 



part of all the known yuccas, altogether forming one of the most 

 complete collections in the world of these Southwestern types ; 

 and he who carefully examines it will he ready to acknowledge it 

 one of the most fascinating of all plant collections. Surely it 

 could have no more fitting home than there in the city of Engel- 

 mann ; and we can not but cherish the hope that no pains will he 

 spared to make the collection even far more complete than it is, 

 and thus give the American botanist a still greater laboratory in 

 which to investigate so great a factor in American plant life. A 

 suggestion of this aspect of the Missouri Garden may be found in 

 the illustrations accompanying the present paper, most of which 

 are from photographs taken there in July, 1892. The magnificent 

 collection of cacti and the several flowering plants of agave in the 

 World's Fair are of the highest interest in this connection. Can 

 not these form a nucleus for a great permanent cactus garden ? 



From the general discussion we may appropriately pass to a 

 more detailed sketch of each of the three groups before us, and in 

 taking them up it will be found most convenient to place them in 

 the order of their evolutionary rank : the cacti first, as represent- 

 ing the higher class of flowering plants; then the agaves; and 

 lastly the yuccas, as somewhat lower in station than the second. 

 This will have the merit, in addition to its logical virtue, of dis- 

 posing of the weightiest group first, and of leaving till the last an 

 amazing little entomological-botanical romance which gathers 

 round the yucca. And the stately agaves will be not inharmoni- 

 ously sandwiched between their two odd brethren. But let this 

 suffice for a prospectus ; the story will tell itself more satisfac- 

 torily. 



"Viewing the three members of our group together, the query 

 presents itself : Is there not some vital significance in the relative 

 extent and diversity of development in these three joint mon- 

 archs of the desert ? Two of them, those we shall consider later, 

 reach only the magnitude of genera, each constituting a moder- 

 ate-sized and not remarkably diversified genus ; while on the 

 other hand the cacti together form an immense family, the natu- 

 ral order Cactacece, aggregating over a thousand species, gath- 

 ered into a number of genera. It is but a grand example of 

 evolutionary principles, "natural selection and the survival of 

 the fittest," for the facts must be interpreted in the light of Dar- 

 win's immortal phrase. The yucca pushes its sturdy rootstock 

 through the sand and drinks up each available drop of water ; 

 the agave's succulent leaves store up a wealth of nutritious sap ; 

 but the cactus seems to be pre-eminently an invulnerable store- 

 house of life-giving moisture, and the veritable offspring of the 

 arid, rocky sand-wastes, while the others seem only adopted chil- 

 dren. Mark the peculiar characters of the typical cactus : The 



