90 



a certain period of their growth, solutions of continuity arc 

 made so naturally and regularly as to preclude the supposition 

 that the dislocation is produced by accident. If we examine 

 them when the shoots are young and vigorous in the early 

 spring, we shall find that there is a faint line externally that 

 marks the position of the future joint, but that internally there 

 is scarcely any indication of its existence. At this time, if we 

 call in the microscope to our aid, we shall find that, at the 

 exterior line of demarcation, there is simply an increased 

 deposit in the cells composing the bark, and a very minute 

 process passing from its inner surface. The line of junction 

 in the interior rarely presents any change more marked than 

 a larger deposit of raphides or crystals there than elsewhere, 

 or occasionally a deposit of some dark resinous material. 

 Iodine, at this time, stains the whole tissue yellow, and scarcely 

 detects the existence of a single granule of starch either in the 

 leaf or stem. 



" At this time the leaves require considerable force to sepa- 

 rate them from the branches, so much so, that we sometimes 

 find that they bring with them some of the wood from the 

 parent stem ; and if a branch is cut off, and dried, the leaves 

 cannot be torn from their attachment 'without great skill 

 and management, showing that the joint is not yet com- 

 plete. By and by, however, a change begins to take place ; 

 with the advance of the season, or from some other cause 

 depending upon the situation and idiosyncrasy of the plant ; 

 the line of demarcation becomes well marked, and the eye can 

 detect it throughout the whole of its course, internally as well 

 as externally. The microscope shows at the same time, that 

 the process of bark, which was at first rudimentary, has gradu- 

 ally . increased, and that an evident change is taking place in 

 the nature of the cells which contain the raphides. Iodine 

 now tinges the proximal side of the junction a deeper lure than 

 the distal, and we begin, here and there, to see a blue dot 

 marking the existence of a starchy mass. 



