LATICIFEROUS CELLS, DEVELOPMENT. 1 97 



are found in the 2nd or 3rd layer of cells beneath the surface. Both series have an 

 almost straight course, and not unfrequenlly they may be followed through their 

 whole length from the node of the embryo to the apex of the root. Before reaching 

 this, they terminate with diminished diameter, measuring hardly half that of the sur- 

 rounding cells. Behind the tapering end the lateral walls are bulged out, with 

 teeth, which fit between the surrounding cells : further back the diameter of the sac 

 increases, the teeth are smoothed down, and their walls are only slightly sinuous : at 

 the top, where the diameter of the sac is not less than that of the surrounding cells, or 

 even greater, its walls are smooth. The appearance of such a sac gives the impression 

 as though it w^ere only with difficulty that it could find room between the cells to push 

 in its apex, and that it endeavours, by extension, to fill up all possible cavities. The 

 surrounding cells may at this time have firmer walls, while those of the tube are 

 soft — therefore the young milk-tubes cling to the surrounding cells, and push out 

 teeth between them. Later the walls of the tubes may become firmer, the in- 

 equalities smooth themselves out, and as the other tissues gain more space, the 

 walls become quite even. Growing in this manner the tubes permeate the ripening 

 embryo to the extreme apex of the root, and reach the seat of its future growth, viz. 

 the limit between the apex of the root and root-cap. 



' In the germinating seed other remarkable phenomena become apparent. 

 While the apices of the laticiferous tubes grew up to this point between the cells of 

 a slowly dividing, and slowly growing tissue, they are now surrounded by a quickly 

 growing tissue, in the focus of growth of the apex of the root. Accordingly they 

 enlarge here to the diameter of the surrounding cells, and even exceed them sometimes, 

 and terminate with bluntly rounded ends, which often appear swollen, at the limit 

 between the root-apex and the root-cap. The ends of the tubes are easily recognised 

 by means of their dense contents; their blunt ends — like plastic masses— are easily 

 found, and clearly marked. But there are never seen even traces of septa in course 

 of solution, which would certainly be found here, if the tubes were formed by 

 the disappearance of the walls separating the cells from one another. From the 

 examination of longitudinal sections through the apices of roots of seedlings, it must 

 certainly be concluded that the laticiferous tubes of the root of Euphorbia have an 

 independent apical growth, and grow on continuously at the apex with the other 

 tissues of the root. 



' At the apical point of the stem the behaviour of the milk-tubes is much more 

 difficult to observe, since they here take a very irregular, crooked course, and there- 

 fore cannot be followed for long distances. Terminations of the tubes are some- 

 times to be found above the youngest leaves, but their connection with tubes lower 

 down could never be proved ^: in the nodes a felt of tubes is always formed, from 

 which branches run up towards the apical cone. There is no evidence against the 

 tubes having here a growth fundamentally similar to that in the apex of the root, and 

 none to support the idea that new milk-cells are successively formed in the growing 

 point, which would subsequently grow out to tubes. 



* It appears as though all the tubes of the Euphorbia plant owe their origin to a 

 process of branching of the original cells formed in the embryo. 



* I was able to prove this repeatedly in E. splendens and trigona.— De Bary. 



