FORMS AND SYSTEMS OF TISSUES. 
85 
lateral branch. The wall of this cell has become so thick that its cavity is reduced 
to a narrow canal. These cells are very abundant in the tissue of Monsterineae, 
and present the appearance, when the petiole is broken across or cut vuith a blunt 
knife, of tough, slender hairs projecting out of the tissue. For idioblasts of this kind 
I propose the term Trkhoblast, in order to express their resemblance to many epi- 
dermal trichomes. Those now referred to have such thick walls that their contents 
are of very little importance from a physiological point of view^, if indeed they do 
not altogether disappear and become replaced by air. But in other cases tliey 
contain latex, w^hich flows out in greater or less abundance w^hen the plant is wounded. 
Such structures, the peculiarities ( f which were first 
recognised by David ^ and compared by him to the 
trichoblasts in the petiole of Monsterineae, and termed 
Laticiferous Cells, were previously confounded with 
true laticiferous vessels which result from a coales- 
cence of cells (see p. 86). The receptacles for latex in 
Euphorbiaceae, Moreae, Apocynaceae, and Asclepiadeae 
are very long cells which are closed on all sides, often 
much branched at the ends, but not communicating 
with one another ; they are formed at an early period, 
near the apex of the stem in the young fundamental 
tissue of the primary cortex, or of the pith when the 
side of the vascular bundles next the pith contains 
phloem [Hoya carnosa) ; in other cases laticiferous cells 
belonging to the cortex put out branches through the 
ring of wood into the pith (Euphorbiaceae, Moreae). 
The laticiferous cells of the leaves are, in the case of 
Euphorbia, only prolongations of those of the inter- 
nodes. The extraordinary length of the laticiferous 
cells, especially in Hoya carnosa, makes it difficult to 
recognise their true nature ; but it is easily explained 
by their early formation near the apex of the stem, 
which necessitates their keeping pace with the growth 
in length of the stem as well as that of the whole 
surface of the leaf. These laticiferous trichoblasts are 
most easily seen in Euphorbia splendens, since they are 
readily isolated in consequence of their thick firm cell- 
wall, and can be distinguished wdth certainty from any 
other form of tissue, by the peculiarity in the form 
of the starch-grains as well as the coagulated latex 
which they contain. The laticiferous cells represented 
in Fig. 71 (slightly magnified and reduced about \ in 
length) have been obtained by allowing the ends of 
branches of Euphorbia sple7idens to decay in water until 
the tissue has become very soft; lumps of the soft 
mass were then dissected with needles under the microscope, and the pulpy tissue 
washed away as completely as possible, until the long laticiferous cells were ex- 
posed, and allowed their closed ends to be fully examined. The structure of the 
laticiferous cells in the leaves can, according to David, be determined with much 
certainty by first extracting with alcohol, and then rendering them transparent by 
boiling in potash. In Ficus elastica the laticiferous cells are thin-walled and more 
Fig. 70. — From a longitudinal section 
through the petiole of Monstera reli- 
giosa: d d parenchymatous cells; j j a tri- 
choblast. 
^ G. David, Ueber die Milchzellcn der Euphorbiaceen, Moreen, Apocyneen, u. Asclepiade 
Dissertation. Breslau 1872. 
