Deciduous 1 

 Lobcf 



Zone of Great 



Surrace 



Expansion 



-Persistent Lobe 

 Secondary Growth 



4 Flakes oP Cork 



Zont of 

 Least Growt In < 



Zone oF Less Growth 



^ ExPoliated Stamens 



Base oF StvUs 



r 



CALYX LOBES AND THEIR SURROUNDINGS (Fig. 12) 



at a in relation to the triangular zone 

 of small cells just below at b. Figs. 

 .^ and 4 are two sections through the 

 same cal^Tc lol^e showing partial ex- 

 foliation. 



It is desirable that a more thorough 

 histological examination be made of 

 more favorable material, i. e., of younger 

 fruits, taken preferably before the cal>Tc 

 lobes begin to "shear off" as well as 

 later. But the evidence at hand is 

 sufficient to warrant the statement 

 that true abscission, either with or 

 without the formation of an abscission 

 layer, does not occur; and that exfolia- 

 tion of the calyx lobes is presumably a 

 continuous i)rocess, although apparently 

 discontinuous. 



The jjrocess of exfoliation is illustrated 

 by the accomi)anying diagram. (Fig. 

 12.) The region f)f greatest growth and 

 consequent surface exj^ansion extends 

 from below the stamens ujjward and 

 beyond the calyx lobes. If the second- 



ary growth of the cells in a cah'x lobe 

 is retarded it must suffer the same fate 

 as the stamens. 



Partial or incomplete exfoliation is 

 probably more frequent than would at 

 first appear. In specimens of both 

 pears and crabs, dead stamens were still 

 adhering to the basin wall below the 

 jiersistent calyx lobes, and the tips of 

 these lobes are usually dead. Persist- 

 ence of a lobe appears to dejx'nd upon 

 the extent of secondary thickening of 

 its basal region.'' In the case of the lobe 

 shown in Fig. 11,3 and 4, exfoliation had 

 begun at one edge, but there was suffi- 

 cient secondary growth within to pre- 

 vent its complete separation from the 

 ovary wall. This indicates that the 

 process of exfoliation is really continuous 

 rather than discontinuous. It is prob- 

 able that with sufiicicnt material all 

 stages of ])artial exfoliation would be 

 found in persistent lobes. However, 

 the matter of continuit >■ or discontinuity 



' In a variety fouiifl on the market in Mi)ntreal, the pit \va.s very shallow. On microscopic 

 examination it was found that there had occurred very little secondary growth, so that for the 

 most part the original epidermis had not been disrupted, except for a short distance below the 

 calyx. The triangular zone of small-celled tissue extended from the bases of the stamens quite 

 to the bottom of the pit. No case of exfoliation of the calyx lobes could be found. It is evident 

 that the accompanying diagram rci)resents adequately only a condition of maximum superficial 

 growth. 



86 



