H. M. Leakb 239 



character of a multiple organ is employed as a plant character, owing 

 to the character, definite for the organ, being indefinite for the plant. 



It is possible, however, to recognise two distinct forms in which the 

 leaves are either all eglandular or all glandular. It is true that an 

 intermediate condition has rarely been observed in which a few of the 

 leaves may bear a minute and rudimentary gland. The condition is, 

 however, extremely rare and though the plant would on direct observa- 

 tion usually be entered as eglandular its true character will be identified 

 through the occurrence of glandular offspring on selfing. 



If plants belonging to a single type and bearing glandular leaves 

 be arranged in series according to the proportion of leaves bearing 1, 2 

 or 3 glands, the series will be practically continuous. Nevertheless it 

 has been found possible to recognise three fairly distinct stages which 

 have received the following notation : 



(1) Glands 1 ; in which all or nearly all the leaves bear a single 

 gland. 



(2) Glands 1 — 3 ; in which the majority of the leaves bear one 

 gland but those of the main stem and possibly one or two of those of 

 the monopodial branches bear three glands. 



(3) Glands 3 — 1 ; in which the majority of the leaves, including 

 all those of the main stem and monopodial branches, bear three glands. 

 A few leaves of the sympodial branches may also bear three glands. 



It has been found possible to isolate and grow in a state of purity 

 forms in which the leaves are eglandular and forms which fall within 

 the third stage as given above. Plants with the leaf glands 1 — 3 on 

 the other hand have invariably given mixed offspring^ 



There remains for consideration the second stage in which the 

 leaves have a single gland only. This too may occur as an intermediate 

 condition between the eglandular form and that with glands 3 — 1, and 

 in such cases does not breed true. It appears probable, however, that 

 it may also occur as a pure form. Within the author's experience 

 plants of type 2 have invariably leaves with one gland, but, for reasons 

 already given, this type has not been very fully investigated and, 

 perhaps, to an extent hardly sufficient to justify the statement that one 

 leaf gland is characteristic of the type though there can be little doubt 

 that a pure form of type 2 so characterised does exist. This pure 

 form with a single leaf gland does not enter further into the present 



' The two cases noted in Table XVIII form apparent exceptions to this statement bat 

 most, in the absence of farther evidence, be considered as extreme instances of divergence 

 from the expected ratio. 



