272 



MORPHOLOGY. 



172 



upon the lower portions, in the Monocotyledons especially, on the vaginal 

 portion of the leaf. A plant of the Oat may be examined just after 

 germination. Here there is a lanceolate, some- 

 what fleshy leaf (scutellum, Auct.) (fig. 172. c.), a 

 vaginal portion (a to ), which includes about a 

 quarter of the whole length of the leaf, and the 

 free border of this vaginal portion which is 

 pushed forward (ligula, b) by the protrusion of 

 the bud. With no imaginable pains can one 

 discover a cause which shall exclude this entire 

 organ from the definition of a leaf, or even make 

 its foliar nature doubtful ; and, disregarding ab- 

 solute size, colour, and fleshy consistence, which 

 vary so abundantly in all foliar organs, there is 

 not the slightest distinction to be found between 

 the cotyledon and the succeeding leaves of the Oat, 

 in the form and arrangement of the parts. If the 

 vaginal portion is shorter, the protruded border 

 somewhat larger, the thing has quite a different 

 name (vagina petiolaris\ and yet is altogether 

 the same : finally, if the vaginal portion is very 

 short, and the protruded border very long, it 

 must be called vagina stipularis, without anything different from the'fore- 

 going being signified. The last two parts are best found, in every 

 possible state of transition, and with them the petiolus alatus, which is 

 also just the same, in the families of the Hydrocharacece, Aracece, Sci- 

 taminecB, &c., in which I have analysed a sufficient number of sources of 

 development. In the bud, where the leaf is only a line, and the vaginal 

 portion half a line long, there can be no doubt about the nature of the 

 so-called vagina stipularis; but when the leaf with the petiole has 

 become two feet long, the vagina stipularis is several inches long, and 

 the vaginal portion, which unites the two, which has remained at only 

 half a line long, gets wholly overlooked in the usual way of examin- 

 ing these things, and the petiole and vagina are taken for two wholly 

 distinct organs. What I have observed in the above-named Leguminosce, 

 in Rosacece, Polygonacece, and some other families, leads immediately to 

 the conclusion that the organs called the sheath of the petiole, winged 

 petiole, ochrea, adherent and free stipules, in the Dicotyledons, are all 

 various forms of one and the same part of the lowest portion of the 

 border of the petiole or leaf, and again are wholly identical in nature and 

 development with the parts named in the Monocotyledons. The so- 

 called free separate stipules have no existence at all ; and, just as in the 

 vagina stipularis, their connection with the petiole is overlooked, 

 because the little piece by which they are connected is so small in propor- 

 tion to the whole leaf, and even to the stipule, that it falls quite into the 

 background. But when the leaf is examined before its cells expand, in 

 the bud, the point of union of the leaf and stipules forms so considerable 

 a portion of the whole length of the leaf, that there can be no more 

 doubt on the subject, that the stipule is a mere appendage of the border 



172 Acena sativa. Germ plant, freed from the albumen, &c. ; viewed in front (left 

 fig.) and at the side in longitudinal section (right fig.), a, Body of the plant (stalk). 

 6, c, Cotyledon. Between a and b, vaginal portion of the cotyledonary leaf; above 

 this the ligule. c, Blade of the cotyledon, d, Outermost leaf of the bud, or plumula. 

 e, Adventitious root, which breaks through the very slightly elongated radicle. 



