408 SECTIONAL TRANSACTIONS.— K* . 



the lower part of the stem are generally sufficient to give the form-class when plotted 

 as percentages of the breast height girth, and the remainder of the curve may be 

 fairly safely taken as representing the shape of the stem above the last possible point 

 of measurement. The greater part of the volume is in the lowest length of the stem, 

 and this is generally measured accurately. 



Dr. E. N. Chrystal and Mr. E. R. Skinner. — The Biology of Xylonomus 

 brachylabris {Hymenoptera, Ichneumonidce), a Parasite of the Larch 

 Longicorn Beetle, Tetropium gahrieli, Weise, and some Studies of the 

 Willow Woodwasp, Xiphydria prolongata Geoffr. (Hymenoptera, 

 Siricidce) and its Parasite Thalessa curvipes Grav. (Hymenoptera, 

 Ichneumonidce) . 

 The larch longicorn beetle (Tetropium gahrieli, Weise) in Britain, its relation to 

 the larch woods and distribution throughout the country. The parasitic insect enemies 

 of this beetle have never been studied in this country, and it is only very recently that 

 a continental worker, Schimitchek, has published a paper upon them. The present 

 paper gives the results of some biological studies on Xylonomus brachylabris carried 

 out at the Imperial Forestry Institute, Oxford, and deals with the pairing and egg- 

 laying habits of the parasite, the attack on the host larva, the cocoon and emergence 

 of the adult. The occurrence of another species of Xylonomus, X. irrigator, as a 

 parasite of T. gabrieli, is also described. 



The studies of the Willow woodwasp, Xiphydria prolongata, Geofif., and its parasite, 

 Thalessa curvipes, Grav., were commenced about two years ago while some work on 

 the Sirex woodwasps and their parasites was in progress. Up to date, the best account 

 extant of the biology of the Willow woodwasps is that by Leisewitz in 1907. Since 

 then nothing further of any note has appeared dealing with their biology. This paper 

 contains a general account of their biology in Britain and some of the observations, 

 especially those referring to oviposition and the egg-stage, are believed to be new. 

 The discovery in 1929 of the Thalessa parasite was the starting point of a further 

 series of observations on its life-history and habits, this parasite being especially 

 interesting in view of the fact that it is closely allied to H, persuasoria L., the large 

 Ichneumonid parasite of the Sirex woodwasps. 



Friday, September 5. 



Discussion on Mineral Elements in Plant Nutrition (see sectional pro- 

 gramme preceding). 



Afternoon. 



Excursion to Long Ashton Research Station. 



Saturday, September 6. 



Excursion to Forest of Dean. 



Monday, September 8. 



Mr. W. H. GuiLLEBAUD. — Experimental Studies on the Artificial Regeneration 

 of Oak. 



An account of experimental investigations dealing with the nursery practice, 

 direct sowing and planting of oak. The work was started in 1927, and the paper is 

 in the main a report of progress. Over seventy series of field plots have been estab- 

 lished in eleven centres in the south of England. In each experiment the treatments 

 are replicated and the plots scattered. 



The chief difficulty experienced in attempting to establish oak by artificial means 

 has been the slow initial growth of the oak plants and their consequent prolonged 

 struggle with the heavy weed growth characteristic of the soils on which oak is usually 



