lxiv INTRODUCTION. 



ders constitute a secondary character of as much importance as any of 

 which botanists have knowledge. 



The substance which surrounds the embryo is called the Albumen, 

 and its absence or presence constitutes a valuable mark of distinction. 

 There can be no doubt that when it exceeds the bulk of the embryo very 

 considerably, as in Ranunculaceee, Papaveraceee, Umbelliferae, Grasses, and 

 the like, it is of such importance, that no plant destitute of albumen is 

 likely to be found appertaining to such orders ; but, on the other hand, I 

 doubt very much whether its presence or absence deserves much attention 

 in orders which are called by German botanists subalbuminous, — that is 

 to say, where the embryo and albumen are of nearly equal bulk ; for it 

 should be remembered, that it always exists in seeds at some period of 

 their existence, and that its remains may very well be expected to be found 

 in almost any seeds ; thus, in fact, both albuminous and exalbuminous 

 seeds are found in Proteacere (Brown in Linn. Trans. 10. 36) ; and even 

 in Rosaceee, which are as free from remains of albumen as any order, it 

 is said to be distinctly present in Neillia, and in others traces are to be seen 

 adhering to the inner membrane of the testa. — The texture of the albu- 

 men is frequently consulted with advantage ; in all Rubiacese it is horny 

 or fleshy; Euphorbiaceee, oily ; Grasses, Polygonese, Chenopodeae, mealy ; 

 in Annonacese, it is ruminated, &c. ; but among Apocyneee, which have 

 solid albumen, it is ruminated in Alyxia. 



The direction of the Embryo within the testa, which is indicated in the 

 ovulum by the foramen, is one of the very few characters to which we 

 know of no exceptions ; and if it were a less obscure point of structure, it 

 would consequently be one of the most useful. For example, in all Cis- 

 tinese, Urticeae, and Polygoneee, the radicle is not turned towards the hi- 

 lum, as in other tribes, but takes an opposite direction ; and these orders 

 are distinguished from their allies by this, better than by any other known 

 character. 



The number of Cotyledons is generally believed to be one of the 

 most important means of distinguishing the great natural divisions called 

 Monocotyledons, Dicotyledons, and Acotyledons ; and it is a most curious 

 fact, that this goes along with anatomical structure. There are, however, 

 plants among Monocotyledons with two cotyledons, as the common 

 "Wheat ; and among Dicotyledons with only one, as Pena3a and some 

 Myrtacese ; and even none, as Cuscuta and Utricularia ; or several, as 

 Schizopetalon in Cruciferse, Benthamia in Boragineoe. Ceratophyllese, and 

 most Coniferae. — To the relative position of the cotyledons there are not 

 the same objections, whence the character of Dicotyledons has been found 

 to consist in the cotyledons being opposite to each other ; of Monocotyle- 

 dons, in their being alternate with each other, if there is more than one ; 

 and of Acotyledons, in germination taking place from no particular point, 

 rather than in their number. 



The only remaining character of vegetation which I find it necessary to no- 

 tice is a singular and very uncommon one, which distinguishes a few small 

 families of planLs. This consists in the presence of theremains of the Amni- 

 os around the embryo in its perfect state : the amnios always surrounds the 

 embryo in an early state, but is most commonly absorbed before the forma- 

 tion of the embryo is completed ; but in Saurureac, Pipercese, and Nym- 

 phaeacese, its remains surround the embryo in the form of a sac, which 

 was mistaken by Richard, who did not understand its nature, for a pecu- 



