Ch. XIII] 



THE DICOTYLEDONS 



551 



plete gradation of forms from mesophytic vines (Pereskia) 

 to extreme xerophytes (globular Echinocactus, Fig. 141), 

 while some return with a different morphology to a semi- 

 mesophytic condition (Phyllocactus, Epiphyllu?n and Rhip- 

 salis, Fig. 142). Their characteristic spines are metamor- 

 phosed leaves. The Prickly Pear, a weed in the sub-tropics, 

 and the Night Blooming Cereus, are the most familiar. 



Fig. 396. — A collection of Cacti, recognizable by their condensed 

 rounded forms, with other succulent plants, in a garden. (From Bailey.) 



Order 23. Myrtales: the Myrtles and kin. About 

 7500 species, mostly tropical, of trees, shrubs, and herbs, 

 having in common an inferior ovary and many stamens, 

 suggestive of Rosales. They include the true Myrtacece, 

 a large and important tropical and sub-tropical family, in 

 which are the Eucalyptus, or Gum Trees (especially de- 

 veloped in Australia, and including the tallest of known 

 plants, page 113), and the Guava. Here also belong the 

 Daphne, a sweet shrub of our greenhouses, the Pomegranate, 

 and the Brazil Nut. The Evening Primrose Family (Ona- 

 gracece) includes the Fuchsia and the (Enothera, one species 

 of which, (E. Lamarckiana, is now famous through the studies 

 of De Vries on mutation. Here also belongs a family of 

 hydrophytes, including the Water Milfoils (Myriophyllum) , 

 of which the Parrot's Feather is one. The Mangroves 



