Scrophulariaceae and Orobanchaceae 147 



ed in size, and in nutritive capacity, till they would become re- 

 duced to relatively small colorless scales. 



Fourth, according as parasitic connection might become ac- 

 centuated with herbaceous plants on one hand or with arbores- 

 cent plants on the other, in corresponding degree might at least 

 two lines of evolution open up; one in which entire plants para- 

 sitic on short-lived herbaceous hosts would become soft and de- 

 graded, while on the other hand, genera parasitic on roots of 

 woody and not least arborescent types, might become in corres- 

 ponding measure perennial and enlarged in the infesting region. 



Detailed comparison will now be made. 



General Morphology of the Root 



In commencing parasitism as shown and illustrated in G. flava 

 (Plate XII, Fig. 1) the matured perennial primary root system 

 is spreading, loose, and expanded, covering a large area. From 

 this expanded primary root system, secondary rootlets pass out- 

 ward and downward and some of these end in parasitic suckers. 

 The roots are firm, strong, fibrous, and play no small part in col- 

 lecting raw material from the soil. The plant still depends large- 

 ly upon crude sap obtained directly from the soil for its susten- 

 ance, and could possibly live an independent existence as Kerner 

 (14, p. 180) has stated for Odontites. 



In G. pedicularia the root system is more condensed and 

 suckers are more abundant. 



In G. purpurea (Plate XII, Fig. 2) the secondary root system, 

 though delicate, is more condensed with numerous sucker en- 

 largements on a variety of plants such as Grasses, Composites, 

 etc. The main root from which these side rootlets arise is con- 

 densed and shortened. 



From the short condensed primary root of G. aphylla (Plate 

 XII, Fig. 3) spring the secondary roots which are less spreading 

 than in the previous two species, wholly indicating a more close- 

 ly dependent parasitism on host roots. These are smaller than 

 the roots previously mentioned, being thin and fibrous with 

 abundant suckers. 



Drawings of the above were made to illustrate natural size as 

 nearly as possible and to show the extent of primary and sec- 

 ondary roots. 



In the transition from the above types the Scrophulariaceae 

 are connected with the Orobanchaceae by the genera Lathraea, 



