UNTERSUCHUNGEN UBER DIE FLECHTENGONIDIEN 189 



" Auswanderungslehre " historically, affording a valuable risumi 

 of previous researches from Sachs (1863) onwards, and con- 

 cluding with tabular details of the author's ash-analyses of various 

 plants of widely-differing affinities ; the respective weights of the 

 various food-materials in the green leaf, and the yellowing, falling 

 leaf are compared. Part ii. (pp. 70-96) deals with the colour- 

 change induced in the leaf before it falls — namely, from green to 

 yellow. The subject is viewed from many points : the arrange- 

 ment of the chlorophyll ; anatomical changes in the leaf-base ; 

 microscopic changes in the chloroplasts ; climatic influences ; 

 effect of anthocyan upon translocation of food-stuffs. This part 

 concludes with the statement that the yellowing of the leaf is 

 not the result of its gradual dying, but a vital process, the visible 

 effect of various physiological changes. Part iii. (pp. 97-117) is 

 entitled " Schlussbetrachtungen," and deals with the general 

 causes of leaf-fall in evei'green plants and in deciduous trees. 

 Finally, the causes of the loss of food-material from leaves before 

 their fall is discussed. This loss, it would seem, is not due to 

 such a simple process as the mere travelling of the substances 

 into the permanent parts, but is an essential portion of the com- 

 plicated changes, structural and chemical, inseparable from the 

 phenomenon of leaf-fall. The subject before us is one aspect of 

 the wider familiar proposition that leaf-fall is essentially a pro- 

 cess concerned with life, not death. And this process is so com- 

 plex, the changes presumably so continuous and covering so long 

 a period, that the observations of a single student, taken even 

 with that scrupulous care of which Dr. Swart's work bears the 

 unmistakable impress, must needs be somewhat unconvincing, if 

 only for the practical limits placed upon their frequency during 

 that period. This book of his is, nevertheless, of considerable 

 historical interest, and is written with a lucidity and conciseness 

 not always common in the work of his countrymen. The author's 

 own results are not very considerable, but they should afford a 

 useful indication of the general lines upon which co-operative 

 research might profitably be directed. 



H. F. Wernham. 



Unters2ichungen iiber die Flechtengonidien. Von Fredr. Elfving. 

 Acta Soc. Sci. Fenn. Helsingfors, 1913. Tom. xliv. No. 2. 

 71 pp. ; 8 plates. 



In this publication Herr Elfving has revived the old con- 

 troversy as to the origin of the green cells or gonidia in the lichen. 

 The dual nature of the thallus has been so long accepted, and has 

 fitted in so exactly with the life conditions of the conjoint organ- 

 isms, that it gives one a considerable shock to be taken back to 

 the position held by Tulasne, and to find it again seriously main- 

 tained that the gonidia are genetically connected with the hyphae. 

 The author has not tested his theory by cultures — which alone 

 would be decisive— but by examination of the growing areas of 

 the thallus. He claims to have seen the different stages of forma- 

 tion of the gonidia in a number of lichens associated with such 



