DI-TRIMEROUS WHORLS AMONG THE FLOWERS OF DICOTYLEDONS. 157 
therefore, assume hypothetically that the primitive ancestors were 5-merous; from 
which Epimedium, Aceranthus, and Jeffersonia, which are 4-merous, were thus derived. 
Of the other genera the four following show gradations :— 
Nandina: Br. S. and P, œ (gradatim mutata) . 3--3 . 1. 
Vancouveria: Br. oo (gradatim mutata) ; 84-3. 343.343.1. 
Berberis: Br. 3; 3+3 . 3+3 . 343.1. 
Diphylleia: 3+3 . 3+3 . 3+3. 1. 
An interesting example of the combination of 5’s and 3’s on the same plant has been 
given by Eichler, who has called attention to the fact that while the formula of the 
ordinary flowers of the raceme of the Barberry is Br. 3; 3+3 . 3+3 . 3+3 .1, when a 
terminal flower is present its formula is 5.5.5.1; i.e. the 2 arrangement *. The 
foliage of Mahonia is $; but the bracts of the inflorescence consist of twenty-one, in 
whorls of threes. The ** cone”’ of buds within stand in six vertical rows. 
Nympheacee have both pentamerous and trimerous whorls, even in the same genus. 
Nuphar luteum: 5 . 5+5 (+10 staminodal) . oo . 5+5 (+20). 
N. advena: 3+3 . (including staminodal) . oo . oo. 
Brassenia: 3+3 . 0 . 12-18 . 6-18. 
Cabomba: 3+3 .0.3+3.3. 
Bentham and Hooker describe the two latter genera as having both calyx and corolla of 
3 members each; but as they are coloured alike, and practically make a perianth, I 
prefer to group them together as derived from a cycle of the } arrangement. 
We thus see that fives and threes not only distinguish different genera but even 
different species of the same genus. 
Magnolia grandiflora supplies a case in which the corolla is often largely increased by 
staminodal petals. The calyx consists of three sessile and imbricated sepals. Then 
follow two or three whorls of three petals each. The petals are large, nearly equalling 
the sepals, but are provided with short claws, never being truly sessile. A variable 
number of “ staminodal " petals (from 1 to 17, but 3 and 15 prevailing, were noticed). 
Referring the whorls to their phyllotactical origins, the leaves are $; the three 
sepals 1; if there be two whorls of petals, they are referable to 2, as explained ; if three 
whorls, to $. The stamens are 33 and the carpels yr- 
The staminodal petals are thus distinguished, inasmuch as they are often very much 
smaller than the true petals, and each stands in the place of a stamen at the end of a 
secondary spiral, leaving a slightly larger scar than does a true stamen; whereas the 
insertion of a true petal occupies a space equal to at least three staminai scars. The 
variation in the number of staminodal petals arises from the fact that besides the last or 
lowermost stamen of a spiral being represented by a small petal, sometimes one or two 
more on the same individual spiral line may be petaloid as well. oF 
Poly gonaceze supply further interesting illustrations of the origin of threes from the 
* See Vine’s < Student’s Text-book of Botany,’ p. 498, fig. 311 [the anther on the left should be on the innermost 
coil and end of the spiral line}, and p. 595. 
tale 
