TRANSACTIONS OF SECTION K. 839 



at all, and tlio latter is as green and liealtliy-looliiDg' at tlio und oi' the normal 

 incubation period as before iuocnlation. 



These observations lend no support to either tlie My coplasm theory of Eriksson, 

 or to any theory which attempts to explain outbreaks of rust to intra-semiual 

 infection handed down froiVi parent to offspring, and the author beUeves that the 

 difficulties hitherto met with in iniderstanding the sudden epidemics of these 

 rust-diseases will disappear as we gain exact information of tlie conditions ot 

 germination, infection, and incubation of the disease-producing parasite ; as also 

 of its habits of lurking in the older leaves of the grass in spots where the produc- 

 tion of a A-ery few spores — quite invisible on a casual overhauling of the grass — ■ 

 prepares the way for more extensive infection as the weather changes. 



On the other hand, they throw considerable light on the question of adaptive 

 parasitism, and show that the previous nutrition of the uredo-spores affects their 

 parasitic power, with regard to another host-species, in much the same way that 

 the previous nutrition affects any other disease germ — e.<j., certain bacteria — or 

 even saprophytes — cjj., certain yeasts and fungi. If only one in a million of the 

 spores once manages to gain a hold on a species or variety hitherto immune, its spore 

 progeny can now successfully attack that species or variety ; and in proportion as it 

 becomes more and more specially adapted to life in the tissues of this new host 

 will it find diihculties in going back to its old host or forwards to another, and 

 so on. 



3. The Pav.t Hintori/ of the Yew in Great Brilaiu and Ireland.^ 

 By Professor H. Conwentz, Dauzir/. 



Many years ago the author studied the distribution of this species, and he has 

 inquired as to the causes of its disappearance in nearly all the countries of the 

 middle and north of Europe; also in the British Isles. It is his opinion that 

 there are three points which prove a previous wider distribution, viz., sub-fossil 

 remains, prehistoric and historic antiquities, and place-names. By microscopical 

 examination he has found a great number of sub-fossil yew trees from submerged 

 forests and other localities in England and Ireland. Then he has examined the 

 prehistoric wooden boxes, buckets, &c., in the British IMuseum, London, in the 

 Science and Art Museum, Dublin, &c., and he has identified more than thirty 

 with Taxtts. Attention is drawn to the names of uninhabited places, which iii 

 former times were very often called after indigenous trees. He has made out a 

 number of some liundreds of English, Scottish, and especially of Irish place- 

 names from the yew which are not unworthy of being considered by botanists. 

 Guided by thi; names of such localities in Germany, he has dug into the ground, 

 and has found sub-fossil remains of the yew. Therefore he has suggested 

 researches of this kind also in the British Isles, and he would be glad to get small 

 pieces of bog wood for examination. 



The genus is not of a considerable geological age, as nearly all Tertiary 

 remains described inider the name of Ta.ius are not yew. 



4. On the Distribution of Certain Forest Trees iti Scotland, as shown by the 

 Imestigation of Post- Glacial Deimsits. By W. N. Niven. 



The information has been chiefly obtained from occasional references in many 

 topographical books of Scotland to the discovery of various trees in particular 

 districts. 



The following arc some of the volumes (about seventy in number) from which 

 information has been derived : — 



'New Statistical Account.' 15 volumes. 1845. 

 ' Old Statistical Account.' 21 volumes. 1791-99. 



' The paper will be published by the Boyal Irish Academy. 



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