Sffl STiTse?] ^oyal Microscopical Society. 157 
which are dissimilar to compound leaves only in the fact that all 
the leaflets have contracted union at their edges to a greater or less 
extent from their origin at the petiole towards their margin. 
Metamorphosed leaves may be considered therefore as a series 
intermediate between the true compound and the true simple lobed 
leaf — a series which forms the connecting-link between the two; 
for a metamorphosed leaf has its leaflets separate in one part, thus 
resemhling a compound leaf ; and its leaflets joined in another part, 
thus resemhling a lohed one. Viewed in this light, a lobed leaf may 
be assumed therefore not as having been divided into a determinate 
number of segments or lobes, designated by the terms flssus, par- 
titus, &c., but rather as a multiple of two or more leaflets which 
have coalesced into one, and which would be more correctly de- 
scribed as double, treble, quadruple, &c., according to the number 
of leaflets which enter into its composition. The leaf of the 
Sycamore, for instance, is composed (according to this hypothesis) 
of five leaflets joined into one ; and a knowledge of its true structure 
and minute venation is better conveyed to the mind by calling it a 
quintuple leaf, the typical leaflets of which are feather-veined and 
joined at their edges, than by using the adjective quinquefid, which 
gives, it is true, a notion of its five radiating ribs, with their respec- 
tive lobes, but conveys no further information whatever as to the 
rest of the veins from which in great measure it derives its cha- 
racter and individuality. 
Simple Entire Leaf. — Simple leaves are classified according to 
their venation ; and are divided into the netted, the feather-veined, 
the ribbed, and the falsely -ribbed. These will be found described 
in botanical works. It is to the two first, however, that our atten- 
tion will be especially directed, because of the frequency of their 
occurrence in their isolated state, and because of their constant 
repetition in composition. 
The true netted leaf is thus described by Lindley : — " The costa 
(midrib) sends forth, alternately right and left, along its whole 
length, ramifications of less dimensions than itself. These I would 
call Vense primarim. They diverge from the costa at various angles, 
and, passing towards the margin of the leaf, curve towards the apex 
in their course, and finally, at some distance within the margin, 
form what is called an anastomosis — a junction with the bark of the 
Vena primaria which lies next them. That part of the Vena pri- 
maria which is between the anastomoses thus described, having a 
curved direction, may be called the Vena arcuata. Between this 
latter and the margin, other veins proceeding from the Vense arcuatse 
occasionally intervene : they may be distinguished by the name of 
l/ense externse. The margin itself and these last are connected by 
a fine net-work of minute veins, which I would distinguish by the 
name of Venulse marginales. From the costa are generally pro- 
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