DUFRENOY: false WITCHES'-BROOMS in ERICACEAE 527 



tricose, or spheroid, as in C. bomis-henricus. Figure 3, d, is the 

 white-seeded form of Chenopodium quinoa of Peru and BoUvia; 

 figure 3, e, the seeds of the European "Good-King-Henry" or 

 "all-good" (C honus-henricus) ; and figure 3, /, the achenes of 

 lambs-quarter (C. album) the black seeds of which are used 

 for food by the Indians of our Southwest, and are grown as a 

 grain-crop in various parts of India. 



BIOLOGY. — The biological significance of false witches^ -brooms 

 in Ericaceous plants. Jean Dufrenoy, Station Biologique 

 d'Arcachon. (Communicated by G. N. Collins.) 



Peculiar shoots showing infection by Exobasidium unedonis 

 Maire + Gloeosporium conviva Maire, have been recorded by 

 Professor Maire on Arbutus unedo in Algeria, and compared by 

 him to \\'itches'-brooms. Other peculiar shoots showing infec- 

 tion by Gloeosperium myrtillus sp. no v. have been seen by the 

 author and similarly compared. 



Witches '-brooms, which had long been considered parasitic 

 infections, are viewed by Vuillemin ('17) as s>anbiotic associa- 

 tions in which profit is derived by both syinbionts, mutually, or 

 at least alternately. "Witches '-brooms are to the shoot what 

 mycon'hizas are to the root." 



In view of this new interpretation, the significance of the 

 "false \\dtches'-brooms" in Ericaceae may be discussed here, 

 from biological data recorded by the author. 



I. Duration of life. Winter dormancy ends sooner in witches'- 

 brooms than in healthy shoots — as recorded by Schellenberg for 

 Firs, Betula, etc. Maire ('16) observed that the false witches'- 

 brooms of Arbutus develop in February in Algeri eh en no 

 healthy shoots have appeared, and also die much soonr, being 

 actually wilted before the normal shoots have finished growing. 

 In Ai'cachon, however, false witches '-brooms were still found 

 living in November. Since the premature death of the brooms 

 in Algeria may be due to lack of water, some discussion of trans- 

 piration conditions is necessary. 



II. Transpiration. It has been assumed that mycelia grow- 

 ing into the vascular strands of witches'-brooms hinder the 



