1922 A TEXTBOOK OF THEORETICAL BOTANY 



Euphrasia, Rhinanthus, Melampyriim, Odontites, Pediciilaris and Bartsia. 

 According to Heinricher these constitute a series of parasitic forms which 

 he considers culminates in Lathraea, now generally included in the 

 Orobanchaceae. We shall discuss the parasitic habit of these genera in 

 Volume IV. 



In addition this sub-family also includes two important non-parasitic 

 genera, Digitalis and Veronica. The genus Digitalis contains some 250 

 species, common in Europe and western Asia, while Veronica is represented 

 by over 200 species which occur chiefly in north temperate regions and also 

 in New Zealand and Australia. The southern species are nearly all shrubby 

 and are separated by many authorities under the generic name of Hebe. 



In Digitalis purpurea (Fig. 1848), the Common Foxglove, the large, 



Fig. 1848. — Digitalis purpurea. Foxglove. 

 Inflorescence. 



purplish flowers are very conspicuous, more especially because they develop 

 in long unilateral racemes. Their shape and the way in which the 

 flowers hang prevent rain from accumulating in the corolla tube. There are 

 nectar guides in the throat of the corolla which take the form of dark 

 purple spots surrounded by white margins. The lower lip is also provided 

 with numerous fine bristle-like hairs. Whether these serve to prevent the 

 entrance of small insects who might steal the nectar, or whether they serve 

 as a grip for large visiting insects is not known, maybe they have both 

 functions. 



Nectar is secreted at the base of the ovary and stored in the base of the 

 corolla tube, which is itself proportioned to the body of a humble bee, the 



