LATICIFEROUS CELLS. 



191 



anastomosis in any well-constituted case ; all their branches, which are often very 

 numerous, end blind (Fig. 84). Anastomoses may occur between their branches in 

 the nodes of many plants (leafy Euphorbias), but this is quite uncertain. Each tube 

 arises, not from a series of coalescing cells, but from one single cell of the meristem, 

 so as to form a 



which grows 



long 



branched sac, and forces its branches be- 

 tween the other tissue-elements. The 

 statements concerning their first develop- 

 ment differ greatly. According to Schmal- 

 hausen's investigations on species of 

 Euphorbia and Asclepiadacese, to be more 

 fully stated below, some few cells of the 

 meristem in the cotyledonary node of the 

 embryo, outside the plerome, are the 

 starting-points of the milk-tubes. These 

 begin, even in the young embryo, to 

 elongate into cylindrical sacs, and to 

 penetrate with their growing ends be- 

 tween the neighbouring cells into the 

 cotyledons and towards the end of the 

 root : they have at an early stage oc- 

 casional branches in the cotyledonary 

 node. AH tubes in the primary cortex, 

 the leaves, and the pith of the mature 

 plant are branches of these few sacs, zvhich 

 are present in the young embryo. From 

 the embryonic stage onwards their ends 

 extend to close (6-8 cells) beneath the 

 primary growing points, and grow on- 

 wards with these, sending branches, which 

 have the same properties, into the lateral 

 buds, leaves, and roots, as soon as these 

 make their appearance. Lastly, they 

 branch further and elongate in the meristem and the young parts so as to form the 

 final system of tubes. The whole plant, e. g, a shrub of Euphorbia the height of a 

 man, has thus only few, much-branched milk-tubes, the ends of the branches of 

 which extend on the one hand into all growing points, and grow with these to 

 an unlimited extent, on the other hand they are distributed in the mature tissues 

 in the manner described, and end blind. As a matter of fact pieces of tubes an 

 inch long, with hundreds of branches, may be teased out of macerated portions of 

 the stem without finding a single anastomosis, or any other blind ending than 

 those of small lateral branches (comp. Fig. 84 A^. 



According to observed facts the possibility cannot be denied, that in later stages 

 of development of a plant, especially in the nodes, single cells of the meristem develope 

 into new milk-tubes, and may coalesce as branches with those which originate from 

 the embryo. However, the occurrence of this phenomenon, if indeed it occurs ai all. 



FIG. 84. — A part of a trunk of a milk-tube, with its stronger 

 branches prepared free and spread out, hardly larger than 

 natural size, from Ihe stem of Euphorbia splendens. All ends 

 0/ irunfc a-^d hyaiirhis are broken off. B from the stem of 

 Ceropegia stapelioides, terminal branches of a non-articulated 

 milk-tube prepared free, wuh numerous blind ends of branches 

 (I45t- 



