174 



LECTURE XT. 



distinguishable by their peculiar contents, the transverse septa become entirely, or in 

 rarer cases {Chelidoniuni) partially absorbed, so that an actual vessel is formed ; at the 

 same time, in many cases, lateral anastomoses are 

 developed, the segments of these vessels sending 

 forth protuberances between the cells of neighbour- 

 ing tissues, which end blindly, or communicate 

 directly with other protuberances of the same kind^ 

 Thus the laticiferous vessels form a reticular system 

 which extends up to the youngest leaves and grow- 

 ing points. If in such plants a subsequent growth 

 in thickness takes place, laticiferous vessels may 

 gradually arise, singly or grouped in layers, as ele- 

 ments of the secondary, cortex between the previ- 

 ously mentioned constituents of the latter (these are 

 particularly abundant in the roots of Taraxacum 

 oßcinale). 



The unsegmented laticiferous vessels, which are 

 at present only known in the Euphorbiaceoe, Ascle- 

 piadese, and Ficus-like plants (Moraceae), arise in 

 quite another way. Schmalhausen showed some 

 years ago that in the young embryo of these plants, 

 at the place where the cotyledons spring from the 

 axis of the seedling, some few (4 — 6) cells, recog- 

 nisable by their contents, are present, which in the 

 further development of the embryo put forth pro- 

 tuberances into the root as well as into the plumule 

 (its axis and leaves). These much branched tubes 

 now penetrate as far as the growing point of the 

 root and shoot, grow continually with these, and 

 become branched with the organs arising from the 

 growing points, just as in the shoot-axes them- 

 selves ; so that thus, in a vigorously developed plant 

 of this kind, the whole system of unsegmented lati- 

 ciferous vessels consists of a few multifariously 

 branched and very long tubes, which were originally 

 simple cells. If it were feasible by any means to 

 destroy all the other tissues of such a plant as a 

 large Euphorbia or Asclepias, the entire form of the 

 plant would still be preserved as a mass of very 

 fine threads of various thickness, representing the 

 ramifications of the original latex-cells; just as the 

 injected vascular system of a vertebrate animal after 

 the removal of all other tissue allows the whole 



Fig. 177.— Latex-cells (unsegmented latici- 

 ferous vessels) oi Euphorbia spUtideiis, prepared 

 free from the apex of a shoot by rotting. A 

 ramifications ending blindly; B a piece more 

 strongly magnified, with 'bone-shaped' starch 

 grains. 



* With respect to these anastomoses of the segmented laticiferous vessels, and the origin of the 

 latter, see W. H. Scott's paper ' Zur Enttmckchingsgcschichtc der gegliederten Milehrohreii' in 

 'Arbeiten des bot. Inst, in Würzburg,' II. 648. 



