PHANEROGAMIA : FLOWERS. 379 



plants ; often quite a thin fluid, as, for instance, in the LemnacecB, where 

 it appears to be little more than a concentrated solution of oxalate of 

 lime (?) with a little gum and sugar ; it is thickest and most tenacious 

 (and probably contains gelatine) in Nuphar, where it very quickly dries 

 up into a thick and very tough membrane. When the secretion is not 

 confined to the surface, but extends to the intercellular passages and 

 spaces of the nearest layers of cells, the secreted substance seems to be 

 always identical. Through this secretion the individual cells, which in 

 the first instance form a solid tissue, become completely isolated from 

 each other. 



These cells* lying beneath the epidermis are usually of a long spindle- 

 shape (e. g. Orchidacece, Onagracece), and about four or five times as broad 

 as the pollen-tubes, hereafter to be spoken of. In the Cucurbitacece, they 

 are very little roundish cells; in the Campanulacece and some others, rather 

 long, but seldom exceed half a French line, and are always distinguish- 

 able from the pollen-tubes by their twice or three times greater diameter. 

 They have been sometimes called mucous tubes, because, by imperfect 

 observations, they have been confounded with the "mucous tubes" of 

 Robert Brown, to be mentioned hereafter, with which they have nothing 

 to do. 



Some of the more remarkable forms of the conducting tissue have 

 received special names, which are in the highest degree superfluous. 

 Thus, in the Plumbaginece, a little cord of such tissue, which has been 

 called an embolus, extends from the internal orifice of the canal of the 

 style to the exostome, lying close beneath. In Linum, Euphorbia, and 

 JRicinuSj the papillae of this tissue are very long and capillary, and extend 

 in a close body over the exostome and into it. They are of a splendid 

 red colour near this in Ricinus. Mirbel first represented them (as well as 

 the embolus just spoken of) in Euphorbia, much too stiffly and twisted 

 like a solid body, which he called an eteignoir. Similar tissue of a beautiful 

 golden yellow occurs in Phytolacca, and in almost all the Portulacece 

 the micropyle is densely covered up by long, capillary, conducting cel- 

 lular tissue. 



I will describe rather more fully the most wonderful structure of the 

 Asclepiadacece and Apocynacece, which has ever been a crux botanophi- 

 lorum, and in which no one has given any useful observations but Robert 

 Brown, f because he was the only one who looked into the mode of the 

 formation of the parts. I have industriously investigated all the plants 

 of this kind that I could obtain, but can, at most, only add in little de- 

 tail points to Robert Brown's excellent essay. In the rudiment of the 

 flower originate two little foliaceous (?) organs, which curve towards 

 each other, and each separately has its margins blended, so that they form 

 two straight tubes. In most Apocynacece they grow together at a very 

 early period ; in few, as in Apocynum, they remain free in the lower 

 part. The upper part, on the contrary, which soon becomes thickened 

 and fleshy, and soon greatly exceeds the lower part in volume, becomes 

 blended into one in both families, so perfectly that at a later epoch the 



* The epithelial cells are mostly of different form from those lying beneath them, 

 and may be distinctly made out in the earlier stages. By the solution of the cells, the 

 epithelial cells are also scattered through the mucilaginous fluid, and can only be dis- 

 covered singly with some difficulty. 



j- How, after Robert Brown's researches, any one can bring forward such clumsy 

 ideas, in the spirit of the last century, as Link (1. c. vol. ii. p. 231. ), is truly only ex- 

 plicable in one way, that the profound study of foreign researches does not yet lie in 

 the spirit of our Botany. 



