460 Facts illustrative of the Cause of Canker, 



cumbering many other series. There is a general tendency in 

 the groups to form themselves into a reentering, or fusiform, 

 series: the same tendency is shown in sets of groups. This 

 causes the greatest difficulty in arrangement; as families which 

 at first appear adjoining, may form the terminating points of the 

 group : when two corresponding groups lie near, the combined 

 effect of relation and affinity is most embarrassing. 



There is, indeed, much difficulty in the formation of natural 

 groups ; and a still greater difficulty in the arrangement of these 

 groups with reference to each other. We cannot call a scheme 

 satisfactory^, until the maximum of allied families is brought 

 together, nor until each family is placed between two others to 

 which it is more nearly related than to any other. The true 

 natural scheme remains to be collected by induction, from a 

 comparison of the arrangement of species in genera, genera in 

 families, and families in groups, alliances, and races. The ma- 

 terials forjudging of these affinities are more numerous than we 

 could have expected ; Sir E. F. Bromhead has enumerated these, 

 or some of them. 



Sir E. F. Bromhead has stated that the object which he has 

 had in view, in forming his sketch of an arrangement, has not 

 been to follow his own judgment, or that of any writer whatso- 

 ever; but to bring together the greatest possible number of 

 admitted affinities, and, if possible, in continuous succession. 

 He considers his sketch as one for future correction, in which 

 certain families and groups may have their places changed ; but 

 that the whole may present something like a fixed basis to work 

 upon, and definite tangible limits of enquiry. He has not cha- 

 racterised any of the races, alliances, or groups that he has 

 formed ; and deems it premature to do so, until some outline of 

 arrangement has been recognised by botanists. His sentiment 

 is, that " Analysis should precede synthesis, and definition follow 

 knowledge." 



Art. V. A fetv Facts illustrative of the Cause of Canker, and other 

 Diseases, in Fruit Trees. By Mr. T. Rivers, jun. 



A FEW facts in the culture of fruit trees have caught my 

 notice, which may perhaps serve in some way to elucidate the 

 cause of canker and disease in those useful occupants of our 

 gardens. The green chisel pear tree, in our soils, is particularly 

 subject to canker, every shoot dying half-way down the season 

 after being produced ; this taking place alike in wet and dry, 

 warm and cold, seasons, and, consequently, the trees, in the course 

 of a few years, getting to be a confused mass of cankered and dead 

 branches, full of moss and disease. Latterly, I have observed 



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