86 
MORPHOLOGY OF TISSUES. 
difficult to follow 
limpid. 
Fig. 
aticifeious cells from the end of a 
branch of Euphorbia splendens, exposed by 
maceration ; A the whole of one and part of 
another laticiferous cell (slightly magnified) ; B a 
piece of one containing starch-grains of peculiar 
form (str. ngly magnified). 
transparent tissue (Fig. 72) 
still more so in the oleander, where also the contents are more 
A Coalescence of Cells arises from the tissue-like union 
of .^iniilar cells, until their contents completely coalesce, 
the partition-walls becoming partially or wholly ab- 
sorbed. In this manner are formed those filiform ag- 
gregates of intercommunicating cells, constituting tubes 
filled with air or sap, which are known as Vessels, such as 
Wood-vessels, Bast-vessels or Sieve-tubes, and Latici- 
ferous Vessels. But roundish groups of cells may also 
coalesce by the absorption of their walls and the forma- 
tion of a single large cavity filled with sap ; these are 
included under the general term Glands (or may be 
specially distinguished as Compound Glands). Just as the 
distinction between idioblasts and true tissue-cells is 
only a progressive one, depending on the augmentation 
of certain characters, so a coalescence is only an extreme 
case of the ordinary behaviour of adjacent cells; the 
contents of these mingle to a certain extent through 
their partition-walls by diff'usion (osmose). Hence we 
frequently meet with tissues consisting of peculiar cells, 
which behave physiologically as if they had coalesced, 
although it is questionable whether the cavities of the 
cells are actually in communication one with another. 
True Laticiferous Vessels are composed of coalescent 
cells containing latex and endowed with the same pro- 
perties as we have already described as belonging to the 
laticiferous cells of Euphorbiaceae, Moreae, Apocynacess, 
and Asclepiadeae. As far as can be judged from obser- 
vations which are not yet brought to a conclusion, these 
vessels originate from rows of cells in the young tissue, 
and especially in the fibro-vascular bundles, coalescing 
at an early stage by the complete disappearance of 
their transverse septa; long tubes (as shown in Fig. 
72) being thus formed filled with latex, which usually 
anastomose with one another laterally, and traverse the 
whole plant in the form of a continuous system of 
tubes ^ 
The Cichoriacese, Campanulacese, and Lobeliaceae 
possess very perfectly developed laticiferous vessels 
belonging to the fibro-vascular bundles, which they 
accompany throughout the whole plant in the form 
of reticulately anastomosing tubes, imbedded, in the 
case of Cichoriaceae in the outer, in that of the 
two other orders in the inner phloem-layer. Their 
form is best recognised by boihng sections of these 
plants for some minutes in dilute potash solution ; the 
anastomosing tubes are then clearly recognised in the 
, and it is easy to expose them entirely in large pieces. In 
^ What follows is founded mainly on Hanstein's researches reported in his Preisschrift, Die 
Milchsaftgefasse und die verwandten Organe der Rinde. Berhn 1864. See also Dippel, Entstehung 
der Milchsaftgefasse und deren Stellung in Gefässbündelsystem. Rotterdam 1865. — Vogel in Jahrb. 
für wis.:. Bot. vol. V. p. 31. 
