88 



MORPHOLOGY OF TISSUES. 



abundant latex in the bulb-scales of Allium Cepa is found in broad elongated rows of 

 cells, whose broad septa exhibit sieve- or latticed structure, but whose actual per- 

 foration is not quite certain (Fig. 73). Where two tubes of this kind lie side 

 by side, the longitudinal walls also show a pitted structure similar to that of im- 

 mature sieve-tubes. These rows of cells traverse the bulb-scales, at whose base they 

 anastomose, as well as the leaves and scapes, in long nearly parallel rows, which are 

 generally separated from the epidermis by from one to three layers of cells. Similar 

 rows are formed by the Utricular Vessels ^ of Amaryllideae, as Narcissus, Leucojum, 

 and Galanthus ; they resemble, moreover, laticiferous vessels in this, that the septa 



of the rows of cells become partially, sometimes 

 entirely, absorbed ; but their sap is not milky, and 

 contains numerous needle-like crystals of calcium 

 oxalate (raphides). Allied to these are numerous 

 other structures in Monocotyledons which bear 

 scarcely any other resemblance to laticiferous ves- 

 sels. In some genera of Liliaceae, as Scilla, Ornitho- 

 galum, and Muscari, the utricular vessels often consist 

 of short interrupted rows of cells, and in the bulbs 

 themselves larger isolated parenchymatous cells, re- 

 sembling the former in containing raphides. That 

 cells containing raphides may, however, unite into 

 tubes, which resemble morphologically laticiferous 

 vessels, is shown in Gommelynaceae. Here rows of 

 cells which are early distinguished from those which 

 surround them by containing raphides arise in the 

 young parenchyma of the fundamental tissue of 

 the internodes and leaves. While their neigh- 

 bours continue to divide, they do not, but re- 

 main unaltered, and their septa are, according to 

 Hanstein, absorbed as the entire organ grows and 

 the cells in consequence elongate. In this man- 

 ner long continuous tubes, filled with raphides 

 of enormous length, are formed from the rows 

 of cells of the fundamental tissue which contain 

 crystals ^. 



As in Monocotyledons we find transitional forms between the imperfect laticiferous 

 vessels of bulb-scales and simple lithocysts which do not contain latex but only 

 raphides; so, on the other hand, Sie've-iubes result from a true coalescence of cells 

 which usually, it is true, contain mucilaginous proteids, but sometimes also latex, as 

 in Acer according to Hanstein, and in Gonvolvulaceae according to Vogel, /. c.^ 



While true laticiferous vessels are confined to a few natural orders. Sieve-tubes, on 

 the contrary, are apparently an'essential constituent of the phloem (bast-portion) of the 

 fibro-vascular bundles. They occur nowhere else, and their morphological structure 

 will therefore be spoken of under the fibro-vascular bundles; we must here speak 



Fig. 73. — Longitudinal section through a bulb- 

 scaie of Allium Cepa; e the epidermis; c the 

 cuticle;)/ parenchyma; sg the latex of the utri- 

 cular vessel coagulated" by potash solution ; q q 

 its septum; the longitudinal wall which separates 

 the utricular vessel from one lying behind it 

 exhibits a pitted structure. 



^ [These vessels were termed 'vesicular' in the 1st edition of this translation. The present 

 rendering, corresponding to the French ' vaisseaux utriculeux,' is a more correct rendering of 

 ' Schlauchgefasse,' and expresses the fact that they are composed of rows of cells (utricles) the cavities 

 of which have not coalesced by the absorption of their septa.] 



^ See Hanstein, /. c. ; also in Monatsber, der Berliner Akad. 1859, 



' la addition to the forms of cells already named, latex occurs also in the intercellular passages 

 of many plants, as Rhus, Alisma Plajitago, &c., and occasionally in the vessels of the wood, as 

 in Carica, some Convolvulacege, &c. On this subject see Trecul, Compt. rend. vol. LXI, 1S65. — 

 Van Tieghem, Ann. des Sci. Nat., 5th ser. vol. VI, 1866. — David, I.e. p. 57. 



