FORMH 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 with a blunt 

 knife, of tough, slender hairs projecting out of the tissue. For idioblasts of this kind 

 I propose the term Trichoblast, 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 they 

 contain latex, which flows out in greater or less abundance when the plant is wounded. 

 Such structures, the peculiarities cf which were first 

 recognised by David ^ and compared by him to the 

 trichoblasts in the petiole of Monsterineae, and termed 

 Latictferous 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 with 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 oi Euphorbia splendens 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 Milchzellen der Euphorbiaceen, Moreen, Apocyneen, u. Asclepiadeen 

 Dissertation. Breslau 1872. 



