112 



MORPHOLOGY OF GYMNOSFERMS 



THE ROOT 



The primary root continues as a strong tap root, with a scanty 

 display of branches (fig. 92), but with numerous small secondary 

 roots. Although dichotomous branching has been thought to be 

 restricted to the secondary roots, under conditions described below, 

 Hill and De Fraine (67) state that in Stangeria the primary root may 

 branch dichotomously. The soil about the roots is full of low algal 



Fig. 92. — Zamia floridana: entire plant, showing strong tap root. 



and fungal forms, and in many, perhaps all, of the genera, some of 

 the secondary roots become infected, in which case they become 

 negatively geotropic. Near the surface of the ground they branch 

 profusely and dichotomously, forming the so-called "root tubercles" 

 which occur in coralloid masses just above or a little below the sur- 

 face (fig. 93). A study of sections shows that the dichotomy so con- 

 spicuous to the naked eye is only apparent, the root apex remaining 

 between the two branches. Reinke (6), SciESfEiDER (18), and 

 Life (31) have contributed mostly to our knowledge of these peculiar 



