TRANSACTIONS OF SECTION K, 831 



The action of artificial digestive fluid is not very reliable as affording a clue to 

 the nattire of the central hody, although it often helps to render its structure more 

 clearly visible vrhen the cells are subsequently stained. 



Some Botanical Photographs from the Malay Peninsula. 

 By R. H. Yapp. 



4. The Diameter Increment of Trees. By A. W. Boethwick, B.Sc. 



There are two methods by which the rate of growth in thickness or diameter 

 increment of trees can be ascertained. One of these methods is to measure 

 annually or at certain intervals the diameter or circumference by means of tree 

 callipers or a tape. The only other method of investigating the diameter incre- 

 ment on standing trees is by means of a very useful instrument known as Pressler's 

 increment-borer. By means of this instrument cylinders of wood, about a quarter 

 of an inch in diameter and from two to six inches long — according to species — can 

 be extracted, and upon those the breadth of the year-rings measured. In order to 

 allow for any irregularity of growth it is safer to take the mean of four cylinders, 

 one from each end of two diameters at right angles to each other. The great 

 diflerence between the two methods is that the latter requires only a few minutes, 

 while tbe former requires years to give reliable results. It is therefore of some 

 interest and importance to know how the results got by both methods agree. But 

 unfortunately, in very few cases have careful measiu'ements extending over a long 

 period of time been carried out. In fact, in the whole history of British arbori- 

 culture there is no other place where more extensive and careful records have been 

 kept than in the Royal Botanic Garden, Edinburgh. So far back as the year 

 1875 the late Sir Robert Christison began a series of systematic girth measure- 

 ments on marked trees in the garden, and since his death in the year 1882 these 

 observations have been carried on by Dr. David Christison, who has recently 

 published some of his interesting results in the * Notes from the Royal Botanic 

 Garden.' 



Through the kindness of Professor Bayley Balfour I have had the rare oppor- 

 tunity of testing whether the increment-borer would yield the same, or approxi- 

 mately the same, results as the tape. On comparing the results obtained by both 

 methods it was extremely interesting to find how closely they coincided. The 

 actual figures are not the same, because the borings were not taken at the same 

 level as the tape measurements. They were purposely taken slightly higher or 

 lower, as seemed expedient, in order not to interfere with the marked circum- 

 ference measured by Dr. Christison. Although the actual figures for each year 

 do not coincide, the mean or average for a period of five or ten years does 

 correspond very closely. 



5. On the Absorption of Ammonia from Polluted Sea-water hy the Ulva 

 latissima. By Professor Letts, D.Sc, Ph.D., and JoriN Haw- 

 THORXE, B.A. 



In a previous research^ it was shown that the occurrence of this sea-weed in 

 quantity in a given locality is associated with the pollution of the sea-water by 

 sewage, the evidence being of three kinds : (1) The high proportion of nitrogen 

 contained in the tissues of the ulva ; (2) an examination of certain localities in 

 which the sea-weed occurs in abundance, and of others from which it is virtually 

 absent ; and (3) experiments on the assimilation of nitrogenous compounds by tlie 

 growing ulva from sea-water artificially polluted. 



Commencing these latter experiments somewhat cautiously, it was first 



• B.A. lieport,l2Q0, and Proe. Rmj. Soc. Edin., 1901, p. 268. 



