TRA^'SACTIONS OF SECTION K. 859 



the host, and of the relationships of each to the other and the environment, to see 

 how it is possible to step in at the critical moment and interfere with these rela- 

 tionships in the direction desired hy human interests. pi?~»v ^4 

 The whole matter thus resolves itself into a study of variation — a purely 

 experimental inquiry into complex hiological relationships, and it is encouraging 

 to see that this is being understood in the large American and other stations, 

 which are distinguishing themselves by their efforts. 



THURSDAY, AUGUST 19. 



The following Reports and Papers were read : — 



1. Report on the Preservation of Plants for Exhibition. 

 See Reports, p.^537. 



2. Report on the Fertilisation of tlie Phoiophycecz. 

 See Reports, p. 537. 



3. The Groicth of the Mycelium of Aecidium graveolens (Shuttlew.) on the 

 Branches of the Witches' Broom on_Berberis vulgaris. By P. Magnus, 

 Berlin. 



Eriksson has stated in the 'Beitrage zur Biologie der Pflanzen (Bd. VIII., 

 Heft I.) that the mycelium of the Aecidium producing the witches' broom of the 

 barbery grew within the cells of the cambium. In the ' Berichte der deutsch. 

 hot. Gesellschaft,' Bd. XV., I asserted that the mycelium was intercellular with 

 haustoria in the pith, cortex, and in the phloem. In the same volume of the 

 ' Berichte,' Eriksson states (pp. 228-231) that he had only examined the cambium, 

 and I only the pith and the cortex, and the latter statement was correct. He also 

 pointed out that he had exammed fresh material, whereas mine had been preserved 

 in alcohol, which objection I did not consider of any value. I have examined, 

 therefore, this summer some fresh material which was kindly sent me by Messrs. 

 Biiumler and Reuter, and have renewed my investigations on the growth of the 

 mycelium in the new shoots of the witches' broom. I find my former statements 

 confirmed. The mycelium grows in the intercellular spaces of the pith, cortex, soft 

 bast, and of the medullary rays, and as I have mentioned {loc. cit.) it often causes 

 the walls of the cells between which it grows to swell up. It sends numerous 

 generally knot-like haustoria into the cells. At the end of April or at the begin- 

 ning of May many of the short rosette-like shoots of the barbery, the leaves of which 

 were covered in spring with aecidia and spermogonia, grow out into long shoots. 

 Into the pith of these shoots the mycelium enters, and it keeps pace with the growth 

 of the medullary cells, so that its ends reach into the meristem of the terminal 

 bud. From the pith the hyphse pass through the medullary rays into the primary 

 cortex, and especially through the original tissue rays opposite the insertion of the 

 leaves. Hence it reaches the axillary buds, and makes its way into their first 

 leaves, which will expand in the next spring. The hyphse which are figured by 

 Eriksson within the cambium cells, I consider to be the cell contents contracted 

 by plasmolysis ; the yellow granules which Eriksson observed in them might, 

 in my opinion, be the first appearance of the yellow colouring matter which fills 

 the young wood-cells of Berberis. 



Lastly, I have to point out that I had identified this aecidium of the barbery 

 in 1875 with Aecidium mm/ellanicum, Berk., and all other observers have followed 

 me in this respect. Since then I have shewn that another aecidium is found in 

 Patagonia and Chili, producing witches' brooms on Berberis huxifolia, and this I 



