20 PROF. JULIUS MACLEOD ON TEN 
clear correlation in the Vegetable Kingdom. The limits of this paper do 
not allow a further discussion of this subject. 
Remark IV.: Gradation may produce, within the limits of one specimen, 
a segregation (disjunetion) of characters, which recalls the segregation 
occurring in Mendelian hybrids.— Example: Adopting the well-known 
presence-absence principle with reference to the visible properties, we 
consider three properties of the leaves of Mnium hornum :— 
(a) In some leaves the vein reaches the summit of the leaf: we call 
this character S. In other leaves of the same stem it does not 
reach the summit (absence of the charaeter) : we call this s. 
(b) Some leaves have marginal teeth: we call this character B. The 
absence of teeth, which is observed in other leaves of the same stem, 
is called b. 
(c) The presence of teeth on the nerve at the back of the leaf is called N. 
In some leaves of the same stem those teeth are absent; their 
absence is called n. 
Table XIII. gives the gradation of the three properties in one stem taken 
at random, only with reference to presence-absence. (See also Table XT.) 
TABLE XIII. 
Mnium hornum, Linn.—Presence-absence table of three characters in the 
leaves of one stem. Interval table. 
Intervals: 1. 2. 3. - B. 5. 6. T: 8. 9. 10. 
BERI ILU E 8 8 8 E E E 8 S S 
1072 PENES "m b b B B B B B B B B 
NEM S A n n N N N N N N N 
Let us suppose now that a species SBN (in all the leaves: midrib reaching 
the summit, teeth at the margin, teeth on the nerve) is crossed with a 
species sbn (nerve ceasing below the summit ; margin and nerve without 
teeth). If the transmission of the properties happens regularly according 
to the Law of Mendel, the plants F, (second hybrid generation) are of eight 
different kinds, viz. : 
SBN, SBn, Sdn, sbn. 
SON, sBn, 
sBN, sbN, 
Of those eight combinations, four occur among the leaves of the stem in 
Table XIII., viz. : 
InantényalB:s1-2 [15 opo hors son. 
PE aAa OA ig. Pesala fs sDn. : e 
N C ad e COUP DAS sBN 
a A 135995... UMS d SBN, 
