290 SUMMARY OF CURRENT RESEARCHES RELATING TO 



plants are wounded, they seek to cover the wound by cork formation, 

 and the varieties able to do this the most quickly are the most immune 

 to the disease. The direct result of wounding is the interference with 

 the currents, and leaf rolling follows ; when the wound is healed the 

 leaf again unfolds. The author proved that the fungus was really the 

 cause of the leaf rolling, and not merely a weak parasite. 



Lichens. 



(By A. Loreain Smith, P.L.S.) 



Study of a Crustaceous Lichen.* — E. Claassenhas made continuous 

 observations on Caloplaca pyracea that appeared on sandstone. The 

 rock was covered at first with the green cells of Cystococcus sp. Later 

 there appeared greyish-white patches on the green, representing the 

 invasion of the lichen fungus. These patches increased centrifugally, 

 leaving in time a bare patch in the centre, which was again gradually 

 covered with the green alga. The lichen fruited abundantly, but 

 wherever it appeared, the green cells were more or less destroyed. 

 Claassen considers the symbiosis to be one of parasitism of the fungus 

 on the algte which grew abundantly before the encroachment of the 

 fungus, whereas the fungus died .off without the nourishment furnished 

 by the alga. 



Study of Cladonia podetia.f — Hans Sattler concludes from an 

 ecological study of the Cladonia thallus, that the podetium is not vegeta- 

 tive, but reproductive in origin. All the Cladonire develop spermogones 

 and carpogones on the same tissue : either on the primary thallus as 

 in C. FloerJceana ; on the scyphus, particularly on the margin ; or in 

 ascyphous forms at the tips of the branches. 



The scyphous and the ascyphous podetia are a morphological develop- 

 ment of the spore-producing tissue to facilitate fertilization of the 

 carpogones by the spermatia. The podetia have originally the function 

 of aiding in spore-distribution by the elevation of the apothecia. 

 Ascyphous podetia arise from a tendency to form spores at a very late 

 stage ; in several cases sterility has ensued, and spore-production is the 

 rare exception. 



Sattler considers that his conclusions support the theory of sexuality 

 in the Cladomacere, as he claims to have proved the true significance of 

 spermogones and apothecia, both being sexually related. In certain cases 

 among scyphous forms, the apothecia are asexual, though in general 

 they are sexual. He considers that the former are derived from the 

 latter, and that within the genus there is a progression from sexual to 

 parthenogenetic spore-development. The assimilating elements of the 

 podetium aid in procuring nourishment, and thus exercise some influence 

 on the form of the podetium. 



* Hedwigia, liv. (1914) pp. 219-20. 



f Hedwigia, liv. (1914) pp. 226-63 (3 pis.). 



