156 
James Small. 
who has investigated the latex of the Compositse more closely than 
any other author, clearly recognised this. He writes (120d, p. 155) 
“ Onjuge en general de Fimportance d’un caractere anatomique i 
sa Constance dans une famille ou une tribe etablie sur d’autres 
caracteres ; cela n’est un moyen certain qu’autant que ces dernieres, 
tir^s le plus souvent des organes reproducteurs, ont valeur reelle.” 
The interpretation of these anatomical facts depends to a large 
extent on the theory which is adopted of the physiological function 
of latex and laticiferous tubes and vessels. Many theories have 
been given, such as the excretion theory of Treviranus, 1827, (see 
124), who compared the laticiferous vessels with gum-resin canals 
That latex is an excretion has been held by De Candolle 
(Physiologie vegetal, 1832) and Richards (Elements de botanique, 
7th edit.). That latex is a secretion with a protective function has 
been held by Schimper (140), Groom (130), Tschirch (150), Kny 
(135), Czapek (120) and Sharpies (142). The analogy of latex to 
the blood suggested by Schultz (1841) was developed by Trecul 
(146), who considered the laticiferous vessels to be “ le systeme 
veineux ” and the xylem vessels to be “ le systeme arteriel.” 
Many others have considered that latex has a nutritive 
function and is translocated, such as Treub (148), Biffen (117) 
who got positive experimental results for the translocation of sugar 
and proteid, Schwendener (141), Faivre (123, 125-6), Jussieu* 
Decaisne, Naudin, Hanstein (132), Schullerus, Haberlandt (131) 
and the writer (143). This theory is opposed by Schimper, Groom 
(130), Kniep (134), Leblois (136) and to a certain extent by 
Mangham (137). 
Spence (145) considers that caoutchouc is a food reserve, rich 
in chemical energy, which is rendered available by oxydases, and he 
compares it with the glycogen in the liver which is broken down 
by glycolytic enzymes. The proteids are rendered available by 
proteolytic enzymes (127-8). That the laticiferous system has 
a dual function, nutritive and excretory, has been held by Sachs 
(Physiol, of Plants) and Faivre (124). Finally, a water-storage 
function has been suggested by Parkin (138). 
The latex-containing elements in the Compositae are cells, sacs 
or vessels. Comparisons in this family and in others, especially in 
the Nymphaeaceae, show that a series of transitions occur even in the 
same genus, from isolated, isodiametric cells containing latex 
through elongated, isolated, latex cells to sacs consisting of two or 
three elongated cells placed end to end, as in Nuphar and 
Nelutnbium, or longer sacs consisting of numerous cells in long 
o.v s, as in Byascnia and Cabomba (144, Vol. I, pp. 48-9). 
