LATICIFEROUS TUBES. I99 



bast are ' latexiferes \' But Schacht's joy at having got rid of the laticiferous vessels 

 and recognising them as branched ' bast-cells,' which he has repeatedly expressed since 

 1 85 1, Mas obviously based upon his failure to recognise the true, delicate milk- tubes 

 in Hoya and herbaceous Euphorbias, a failure which had less excuse at his time; 

 further upon the opinion that the latex of these plants was contained in the thick- 

 walled sclerenchymatous fibres, which are often branched, and upon cognate and 

 further confusion of the latter with the well-distinguished thick-walled milk-tubes of 

 Nerium and succulent Euphorbias. 



Finally, it is undeniable that in the family of the Papaverace^e, in the Aroidese, 

 and Musaceae, there is a near relation between the milk- tubes and peculiar sacs con- 

 taining colouring matters and tannin. In the first the milk-tubes are absent in the 

 rhizome of Sanguinaria, in Glaucium, Macleya, and the sacs containing colouring 

 matter appear in their place : the other above-named genera are without these, and 

 have laticiferous tubes. All those Aroideae and ^Nlusaceae which have been examined 

 have tannin-sacs, variously distributed; in certain forms there are also found milk- 

 tubes extremely rich in tannin, in place of which in many Aroideae there are only rows 

 of tannin-sacs. (On this point compare also Chap. XII.) All these anatomical 

 relations remain inexplicable, till we know better than at present the physiological 

 significance of their different contents. Here we cannot do more than draw attention 

 to them. The anatomical facts above mentioned suggest that under the name INIilk- 

 tubes there are at present united two sorts of structures, which do not correspond in 

 function, namely, in the first place those of the Aroideae and Musaceae, containing 

 more especially tannin ; on the other those of other milky plants, which have little 

 or no tannin, and which are closely related to the sieve-tubes. 



' Mirbel, Exposition de ma theorie, &c., Paris, 1809, p. 247, &c. — Idem, Ann. Sci. Nat. 2 ser. 

 torn. III. p. 143. 



