Scrophulariaceae and Orobanchaceae 171 



Tozzia parasitizes on the roots of Ranunculus, Petasites, Rumex, 

 and Alchemilla. 



Poa, Avena, Luzula, Carex, Senecio, Trifolium, Capsella, Epi- 

 lobium, and Festuca, are given by Heinricher as hosts of Euph- 

 rasia. 



The roots of Lathraea may attach themselves to the roots of 

 Ash, Elm, Poplar, Hornbeam, and Hazel as hosts. 



Species of Orobanche seem to have a very wide range of hosts. 

 According to Koch (16), Orobanche minor may parasitize on 44 

 species of plants; 0. ramosa on 29 species; 0. speciosa on 13 

 species, and 0. hederae on 3 species. These hosts may be found 

 amongst members of Papilionaceae, Geraniaceae, Cruciferae, 

 Oleaceae, Ranunculaceae, and others. 



Although various species have been given as hosts of Aphyllon, 

 the writer quite agrees with Smith in finding it to grow only on 

 the roots of Aster corymbosum. 



Epiphegus has been found to grow only on the roots of Fagus 

 americana. Conopholis similarly parasitizes on but the one 

 genus Quercus, and so far as the writer has learned on the group 

 of the red oaks. 



The writer feels deeply indebted to Professor John M. Mac- 

 farlane who first suggested the work and whose valuable criti- 

 cisms, and assistance have been a source of constant encour- 

 agement in the preparation of this paper. Thanks are due to 

 Mr. W. R. Taylor for the photographs in Plate XVI, to Dr. F. 

 W. Pennell for the use of several slides, and to Mr. H. W. Stout 

 for locating a growth of Conopholis. 



Summary 



A short review of the evidences dealt with above might be 

 put in summary form as follows: 



1. All macroscopic and microscopic details suggest that the 

 parasitic Scrophulariaceae and Orobanchaceae form a contin- 

 uous and parasitically degrading morphological series that show 

 transitional steps from green nearly autotrophic plants like 

 Melampyrum, Rhinanthus, and Euphrasia to increasingly con- 

 densed and degraded genera like Bartsia and Harveya, on to 

 Lathraea, that has been shown to be placed by some botanists 

 in Scrophulariaceae, by others in Orobanchaceae, thence through 

 species of Orobanche to Epiphegus, and finally Aphyllon and 



