92 MR. MIERS ON THE OUTER FLESHY COVERING OF THE SEED 
quoted (p. 31), as an instance of the progressive formation of the false aril, he describes 
and figures (in plate 2. figs. 7 & 8) the ovule of Clusia flava, which he examined after the 
fall of the corolla, at which period he observed that the primine adjoining the funicle 
became enveloped for a quarter of its length by a cup-shaped arilliform process, and there 
can be little doubt that this expands into the entire fleshy coating, which at a later 
period we know envelopes the testa in the manner I have described in the Clusiee. 
M. Dutrochet, a very able physiological botanist, in discussing the nature of the aril, 
denies that its growth proceeds immediately from the placenta, and declares his convic- 
tion, formed after many years of patient investigation of the subject, in the following 
words :—“ L'opinion qui me paraît aujourd'hui la plus conforme å l'observation, est que 
l'arille est une extension de la partie inférieure ou de l'enveloppe corticale du funicule*.” 
Mirbel has furnished us with evidence of great importance in the solution of this 
inquiry: he minutely describes the growth and development of the ovule of Cueumis 
Anguria, in which he observed, after the period of its fertilization, the production of two 
distinct layers of cellular tissue over the primine, originating, no doubt, from an emana- 
tion and extension of the placentary funicle. His words are, “deux couches de tissu 
cellulaire, qui n’appartient pas primitivement à l’ovule, mais qui s’applique à sa surface 
et finit par lui servir d’enveloppe comme ses téguments proprest," thus affording un- 
questionable evidence of the extraneous growth of the arilline, evidence since confirmed 
by the observations of Gasparini and Planchon. I shall be able to show that the crusta- 
ceous tunic of the seeds of the Queurbitaceæ, hitherto held to be the testa, as well as its 
immediate soft envelope, are both of arilliform origin, and that the true integuments 
resulting from the primine and secundine of the ovule are to be found in the membrane 
that immediately invests the embryo, and which has always been considered the tegmen : 
this fact is attended by some curious phænomena which will be detailed in another place, 
where I will adduce many instances of the anomalous development of the raphe. I will, 
however, here allude to the peculiar structure of the outer tunics in many of the Cucur- 
bitacee : if the seeds of Citrullus, for example, be macerated in water, the outer shell 
will be found to eonsist of three distinct parts, which may be termed the epiderm, the 
ert ni — The epiderm is pellicular, transparent, and under the 
band ct are =- ze: reticulstions; the mesoderm is always fleshy, and 
ee mes SER = en mixed with pleurenchymatous deposits; the 
ylitders : cime: as m e eus 1s crustaceous, and consiste of transverse hollow 
iron RS = == = utinated together. The epiderm is a continuation, 
naine ee Dr sheath of the umbilical cord; the mesoderm is 
protect the more delicate s lint y agite cosi essa pres i ies in 
dietiust-depodt: sithi im "m die the raphe; but the crustaceous endoderm is a 
sac, enclosing the seed, and de ie er Forming å compressed and søger 
space filled with loose cellular tiene pus dts mouth (the hilum), within which is a 
sitrfned of the-eridoderin v iden which is also generally extended over the internal 
the’ fertilization of the pe — deposits must be formed at a period subsequent to 
» as will be evident from the copious details, illustrated by 
* Mém. Mus. se 
~ + Mém. Acad. Paris, ix. 622. tab. 1. fig. 10 e; fig. 11 4. 
