LIFE FORMS OF STKAND PLANTS. 



385 



secondary roots). — This mode of growth is exemplified in Rubus vil- 

 losus (canadensis) and ]\. trivialis, in most of the woody lianas (when 

 unable to find supporting objects), and in two herbaceous species 

 of Leguminosae, Phaseolus helvolus and Bradbury a (Centrosema) 

 virginiana,. 1 



3. The radiant form, which may be regarded as a phase of the pre- 

 ceding, is exhibited by certain — chiefly annual — species (fig. 72), pos- 

 sessing a well-defined vertical taproot, which is either slender (as in 

 Mollugo veriicillata, Euphorbia polygonifolia, Diodia teres) or rather 







jr j«* i- .-" . I " 



**^ 



Fig 



-Diodia teres on the middle dunes near Oceanview, Va., illustrating the radiant form 



stout (as in hechea maritima, Oenothera humifusa, Meibomia areni- 

 cola, Cahile edentula). In this form the stem branches at the surface 

 of the ground, and the branches, lying flat upon the sand (only the 



1 The Pes-caprae vegetation form, which has creeping stems sending numerous 

 secondary roots into the soil, may, perhaps, l:e regarded as a further development 

 of this habit. It is a form very characteristic of the tropical strand, but hardly 

 not represented on the Virginia coast. Farther south, near Cape Hatteras. 

 humble representatives of it occur on the edges of the salt marsh. On the coast 

 of Georgia the species which gives a name to this form, Ipomoea pes-caprae, 

 reaches its northern limit in America. 



