666 



BOTANY 



pletely parasitic form is Lathraea (cf. p. 211), the species of which have no trace of 

 chlorophyll ; L. squamaria, the Toothwort, is parasitic on the roots of the Hazel. 

 Many (e.g. Tozzia, Bartsia, Euphrasia, Odontites, Pedicular is, Melampyrum, 

 Aledorolophus) are semiparasitic. Although they possess green leaves they attach 

 themselves by means of haustoria to the roots of other plants, from which they 

 obtain nutrient materials. Further details regarding the mode of life and develop- 

 ment of these forms, and the seasonal dimorphism they exhibit, will be found in 

 the literature cited ( ss ). 



OFFICIAL. Diyitalis purpurea yields DIGITALIS FOLIA. 



Family 3. Orobanchaceae. Root-parasites, without chlorophyll. Flower as 



V\<: 743. Nicotiana taltncum. a, Flower ; b, corolla, cut open and spread out flat ; c, ovary ; 

 rf and e, young fruit, (a, d, c, nat. size ; e, d, x 2.) 



in the Scrophulariaceae, but with a unilocular ovary. Several British species of 

 Orobanchc, parasitic on various host plants (Fig. 749). 



Family 4. Bignoniaceae. Woody plants, in many cases climbers. Stamens 4, 

 corolla two-lipped. Seeds winged. Catalpa bignonioides, Tecoma radicans, orna- 

 mental plants from X. America. 



Family 5. Gesneriaceae. Tropical herbs with a unilocular ovary which is some- 

 times superior, in other cases inferior, and 4 or 2 stamens. Frequently cultivated 

 on account of the beautiful colour of their flowers, e.g. Gloxinia, Aeschynanthus, 

 Achimenes. Ramondia pyrenaica is one of the few European representatives. 

 Streptocarpus ( w ) polyanthus only develops one of its cotyledons, which persists 

 and attains a large size ; the inflorescences arise at the base of the cotyledon. 



