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 (Pig. 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 Amaryllidese, as Narcissus, Leucojum, 
and Galanthus ; they resemble, moreover, laticiferous vessels in this, that the septa 
of the rovv^s 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 Commelynacese, 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-tuhes 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 Convolvulacese according to Vogel, /. 
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 
^ [These vessels were termed 'vesicular' in the ist 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. 
^ In addition to the forms of cells already named, latex occurs also in the intercellular passages 
of many plants, as Rhus, Alisma Plantago, &c., and occasionally in the vessels of the wood, as 
in Carica, some Convolvulacese, &c. On this subject see Trecul, Compt. rend. vol. LXI, 1865. — 
Van Tieghem, Ann. des Sei. Nat., 5th ser, vol. VI, 1866. — David, I.e. p. 57. 
Fig. 73. — Longitudinal section tlirough a bulb- 
scale of AlUic7n 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. 
