INSECTIVOROUS PLANTS 267 



infection of the root system in the soil. This is, in fact, 

 practically certain to take place in soils where former 

 generations of the species have grown. We may recall 

 here that the Lolium temulentiim symbiosis is also congenital. 



§ 5. Insectivorous Plants 



" Scarcely another region of botany has in recent times 

 had so much attention drawn to it in wider circles as the 

 so-called Insectivorous Plants ; and this is chiefly due to 

 Darwin's extensive work, which has given rise to many 

 accounts." So writes Goebel at the opening of his own 

 memoir on Insectivores in his " Pfanzenbiologische Schilde- 

 rungen," a work which must share the honour with Darwin's 

 book on " Insectivorous Plants " as providing the solid 

 ground of our knowledge of this quaint group. 



Systematic. — Insectivorous plants belong to five different 

 families, {a) The Droseraceae include 5 genera and about 

 100 species, of which some 90 belong to the genus Drosera, 

 the sundews. The most familiar of the insectivores, 

 Drosera, and the most famous, Dioncea muscipula, the Venus 

 fly-trap, both belong to this family, (b) The Nepenthaceae, 

 pitcher plants, include a single genus. Nepenthes, with 

 about 50 species, (c) The Sarraceniacece^ American 

 pitcher plants, include 3 genera and about 10 species. 

 {d) The Cephalotacece are represented by a single species 

 inhabiting Australia. These four families stand near each 

 other in the natural system ; they all belong to the Archi- 

 chlamydeas. {e) Among the Metachlamydeae there is the 

 single insectivorous family, the Lentibulariacece , with 5 

 genera and about 300 species, the great majority of which 

 belong to the genus Utncularia, comprising the bladder- 

 worts, while the genus Pinguiciila, comprising the butter- 

 worts, comes second in point of numbers. These two genera 

 include familiar British species. The insectivores thus form 

 two small groups far apart in the phylogenetic system. The 

 habit has arisen twice at least in evolution. It is probable 

 that its origins are much more numerous than this, for, in 



