Origin and Development of the Composites. 157 
Numerous cases of transitions from such sacs to vessels are 
known; the vessels, indeed, frequently show the sac stage before the 
walls break down to produce the typical anastomosing system. 
Transitions between vessels and tubes are recorded for Hevea and 
Manihot (Euphorbiaceae) and for Tupa salicifolia (Lobeliaceze), cp. 
Trdcul, 146, Tome VII, p. 178. Transitions from the common oleo- 
resin canals of the Composite to laticiferous vessels are recorded 
by Trecul (op. cit., p. 181) in Gundelia Tournefortii of which he 
remarks “ Ces vaisseaux donnent done un degre de transition de 
plus entre le canaux oleo-resineux des autres Composes et les 
laticiferes les plus parfaits.” See also 137a for somewhat similar 
canals in the primary and secondary phloem of Rhus. 
Cells containing oleo-resins are so common in higher plants as 
excretory organs that the widespread occurrence of cells which 
also contain reserve proteid and carbohydrate does not call for 
any particular explanation. 
The elongation of these cells and their organisation into 
sacs and vessels, with the extreme and peculiar case of the 
development of tubes instead of vessels, is best regarded as part 
of the epharmonic variation which produces climbing plants. 
Before developing this suggestion it will be advisable to 
consider the function of laticiferous tissue in general. The oleo- 
resin cells are in the first place mere receptacles for excretory 
products; the same may be said of these cells as Record says of 
resin tracheids (139), i.e. they “represent one form of reservoir 
for excretions.” The addition of reserve food material — proteid (129), 
etc., caoutchouc (145), carbohydrate, etc.—need not change or 
eliminate the excretory function. The second class of material 
is rendered available for immediate use by specific enzymes, which 
would separate the secretions from the excretions by solution 
and diffusion. The simple, isolated latex cell has, therefore, two 
functions ; it is a receptacle for excretions and for food reserves. 
The organisation of the cells into sacs produces no change in 
this duality of function. The food reserves still require to be 
dissolved before they can pass from one cell to another, from one 
part of the plant to another. The breaking down of the dividing walls 
when the sacs become vessels renders possible the translocation of 
the solid materials from one part of the vessel to another part of the 
same vessel no matter how distant it may be. That such 
translocation of solids does take place is considered proved for 
Lactuca by the preliminary experiments described by the writer 
(143). That translocation of sugars in solution takes place is 
proved for Euphorbia by Biffen’s quantitative analysis of the sugar- 
