230 THE BIOLOGY OF FLOWERING PLANTS 



It seems certain that they are food-storage organs. Goebel 

 regards the excretion of water by the glands as a substitute 

 for transpiration. The amount of water given off and 

 finding its way to the soil through the opening of the scale 

 may be large. Chemin (1920) has determined it at 3 to 4 per 

 cent, of the weight of the plant in twenty-four hours. He 

 regards the excretion as getting rid of superfluous phos- 

 phates, sulphates, and ammonia — a somewhat improbable 

 explanation. It has also been suggested that small soil 

 organisms — protozoans, diatoms, worms— find their way into 

 the leaf hollows and are digested and absorbed by the 

 plant, but no proof of this exists. It may be noted that the 

 subterranean leaves of Tozzia show features like those of 

 Lathraea in a simpler form. The margins are bent back, 

 and in the hollow thus produced water-excreting glands 

 are found. 



According to Heinricher (19 10) the seed of Lathraea 

 cannot germinate without contact with the host roots, but 

 the process is not adequately known. The two cotyledons 

 are unfolded and a true root with side roots develops. 

 On the root arise numerous disc-like suckers, whether in 

 response to the stimulus of a host root, to the stimulus of 

 contact with solid particles, or spontaneously, has not been 

 definitely settled. The suckers are proliferations of the 

 cortical tissue of the root. In contact with a host root they 

 spread out over it or almost enclose it, becoming fixed by 

 numerous unicellular filaments like root-hairs. An absorb- 

 ing process, dissolving its way through the cortical tissues, 

 penetrates to the wood. Connection between the wood of 

 the host and of the parasite is made by the development 

 in the sucker of a strand of tracheids ; other prosenchymatous 

 cells make contact with the parenchyma and the bast. 



The Lathraeas have a certain amount of latitude as regards 

 host plants ; normally they occur in shady places where 

 they parasitise the roots of woody plants, L. Squamaria 

 affecting in particular the hazel. 



Broom-rapes. — The Lathraeas lead to the Orobanchacese, 

 in which family they are sometimes placed. The family 



