356 Mr Gorry, On some jwints in the structure and [Ap. 30, 



generally, terms the "constant resin-canals." They follow the course 

 of the fibrovascular bundle from the stem into the leaf and join 

 in the stem, the main cortical resin -canals running longitudinally 

 from below upwards parallel to the fibrovascular bundles. 



Beside these numerous other smaller resin-passages are to be 

 met with in the leaf, the number of which is very inconstant but 

 often there are nine or ten of them, the three most frequently pre- 

 sent being an unpaired median, one in the centre of the flat upper 

 surface, and one on each side of the lower surface equidistant from 

 those at the ends and also from the median ventral line of the 

 leaf. These inconstant resin-ducts do not all appear simultane- 

 ously but have a definite order of sequence, those on the upper 

 surface always appearing last. They disappear also towards the 

 apex of the leaf in the same order in which they appear, and at the 

 extreme point only the two constant ones are to be found. 

 Their mode of formation is as follows : 



At a very early stage indeed in the history of the leaf when all 

 the cells are still in a meristematic condition and long before the 

 first trace of the formation of the guard-cells of the stomata can be 

 distinguished the origin of the resin-ducts may be observed in the 

 palisade tissue. 



In the position where a resin-duct is about to be formed a single 

 cell may in transverse section be seen lying in the midst of the 

 large chlorophyll-containing cells of the cortical parenchyma, but 

 differing from these latter slightly in size, form, and markedly in 

 being filled with very granular protoplasm which is destitute of 

 chlorophyll grains and is therefore colourless. This is the mother- 

 cell of the resin-duct. 



This mother-cell divides first into two semicircular segments by 

 means of a longitudinal wall, and then each of the segments in turn 

 divides into two by a wall in the same direction as the first wall 

 but in a plane perpendicular to it. Thus a group of four quadrant 

 shaped daughter-cells is produced, each containing protoplasm and a 

 nucleus. These four cells then enlarge, after which they tend to 

 round off slightly, and, in consequence of this, certain of the parti- 

 tion-walls split and separate from each other at the common point 

 of union or convergence of the cells. This separation takes place 

 very gradually and slightly at first, and its result is a small inter- 

 cellular space which is the cavity or canal of the resin-passage. 

 Before this separation takes place however, some at least, and 

 often all of the four daughter-cells begin to divide by walls in a 

 direction tangential to their common point of convergence, and so 

 a circle of cells immediately exterior to those which surround the 

 canal of the resin passage, and form the resin-wall is produced. 

 Neither these nor the cells of the resin-wall ever contain chlorophyll 

 grains at any stage. Owing to the enlargement of the cells of the 



