AS AIDS IN THE DETERMINATION OF SPECIES. 47 



weighed, amounting to a little over 200 grains. They were distilled by passing a 

 current of steam through them for some time, but not a trace of oil, not even the 

 smell of it, was obtained. 



Hence it would appear that the volatile oil is confined to the leaf blade, the 

 flower-buds, and the fruit-capsules. 



The presence of central canals or reservoirs throughout the length of the petiole 

 in calophvUa, and its close ally ficifoUa, macnlata, and its yariety cifj'iodora, it is not 

 easy to explain. When it is known whether they occur in any, and in what other 

 forms, one may perhaps venture on an explanation. It is noteworthy that in 

 calophylla the kino is a liquid of treacle-like consistence, and obtained in considerable 

 quantity by tapping the tree (Euc. Dec. X.), and that oi macnlata is readily soluble 

 in hot water (Dec. III.) 



While weighing the leaf-stalks for the above purpose the weight of the leaf-blades 

 belonging to them was likewise determined. The blades were sometimes imperfect 

 from the ravages of insects or decay, so that the relative weight errs on the side of 

 defect ; 1000 leaf-blades were found to weigh 4832|grs., and the corresponding leaf- 

 stalks 212grs., so that, on an average, each stalk has to bear a weight at least 23 times 

 that of its own. 



VI. A Practical Test. 



In order to settle how far the transverse section of the petiole alone was capable 

 of determining species, we decided to submit the matter to a practical and very 

 searching test. The names of the 30 kinds investigated by us were handed to Mr. 

 Guilfoyle, and he selected specimens of leaves of six of them. These were sent to 

 us with numbers attached, while the names were retained by him. It will be seen 

 that the test was really very severe, even more so than would occur in actual practice. 

 In the first place the locality of the tree would be known, when met with in its native 

 state, and by referring to the Table of Geographical Distril-ution (Table I.), the area 

 of selection would be limited. In the next place, there are certain characters belong- 

 ing to the leaf as a whole, which would help to settle specific nature. These two 

 features are taken into account in the next section, dealing with a scheme for deter- 

 mining species, but we thought it well to settle how far anatomic structure of the 

 leaf-stalk, apart from other characters, could be depended on for specific distinction. 

 This trial justifies us in our belief, that while sections of the leaf-stalk may be 

 valuable atds in the discrimination of species, it would be imsafe to rely upon them 

 exclusively. 



