Notes . 
167 
involution occurs (/), as in Nepenthes, and between this and the upper 
limit of the sheath there appears a median, slightly projecting longi- 
tudinal ridge, which ultimately develops into the median adaxial flap. 
It appears at first as a simple ridge, and I see in its development no 
ground for concluding that it ‘results from fusion of two leaflets 1 / 
Dr. Macfarlane has sought for support of his view as to its compound 
character in its internal structure, and has cited the case of Iris, saying 
that the leaf of Iris has long been known to be composed of £ opposite 
leaf-lobes, whose faces are not only applied to each other, but organi- 
cally fused/ But this view is surely altogether a thing of the past, 
since Goebel demonstrated 2 that in its development the leaf of Iris 
shows no indication of a composite nature ; the ensiform portion is 
rather to be regarded as an outgrowth of the abaxial side of the leaf, 
which far overtops its organic apex. I have elsewhere pointed out 3 
that anatomical evidence is insecure, and in the absence of evidence 
from external form, the mere fact of the arrangement of the vascular 
bundles being such that their xylem-masses face one another is quite 
insufficient foundation for a hypothesis of origin by cohesion of 
parts. Moreover, in the case of the phyllodes of various species of 
Acacia , the arrangement of the vascular bundles is similar to that in 
Iris, or in the flap of Sarracenia ; if the vascular arrangement is to be 
admitted as evidence of coalescence in Sarracenia , these leaves also 
would demand a similar explanation, which in Acacia appears even 
less probable than in those above quoted. 
I conclude therefore that a hypothesis of cohesion is unnecessary for 
the explanation of the adaxial flap of the leaf of Sarracenia , it would 
appear to me to be a simple outgrowth in a radial plane, somewhat 
similar to that of the leaf of Iris, or the phyllode of Acacia ; at all 
events, its formation by coalescence of leaflets or pinnae is out of the 
question in the absence of any evidence for such a view in the con- 
formation of the young leaf. 
As regards the lid in Sarracenia, I see no reason to think this is more 
than a simple flattened apex of the leaf; neither the development nor the 
mature structure gives sufficient evidence of a compound nature. Thus 
I should conclude that the leaf of Sarracenia is throughout a simple 
phyllopodium, consisting of (1) a basal sheathing portion, (2) a middle 
portion which may be hollowed by involution of the upper surface, and 
1 L. c. p. 262. 2 Bot. Zeit. 1881, p. 96. 
3 Annals of Botany, vol. i, p. 1 34, etc. 
