158 
James Small. 
- content of the latex in undarkened and darkened leaves (117). 
That both sugars and proteids are manufactured in the leaf and 
pass at once into the laticiferous vessels or tubes is rendered very 
probable by the above experiments, by the fact recorded by Biffen 
(loc.cit.) and others that the blind-endings of the laticiferous system 
are generally connected with the palisade cells of the chlorenchyma, 
and by the fact that in the Composite “ it often happens that the 
laticiferous ducts are actual sieve tubes or are at least continuous 
with elements of that nature ” (133, p. 433). 
Laticiferous tubes can be considered as a special development 
of the vessels. The first stage is seen in Tupa salici/olia, where 
some of the cells comprising the vessel are branched. 
The conclusion from the known facts is then that the tubes or 
vessels forming the laticiferous system exercise two functions; 
they are reservoirs for excretory products and at the same time are 
canals along which food materials can be easily and rapidly 
translocated to considerable distances either in solution or in the 
solid condition, and in which these same substances can also be 
stored until required. 
If an explanation is sought for the development of this parti¬ 
cular method of translocation in some groups of plants and not in 
others, the general prevalence of the climbing habit in those groups 
which show laticiferous tissue becomes significant. The four 
families in which laticiferous tubes occur, Euphorbiaceae, Moracese, 
Apocynacese and Asclepiadaceae, are well known to contain quite 
a number of climbing species. The same is true of many of the 
groups in which laticiferous vessels occur, e.g., Araceae, 
Convolvulaceae, Lobelioideae and Clusioideae (cp. Trecul, 146). 
Other families which show laticiferous sacs or vessels, such as the 
Nympheaceae and Musaceae, are herbs which develop long stems, 
petioles or peduncles by rapid growth. It is of interest to note 
also that in the Gymnosperms one of the few genera with many 
climbing species, Gnetum, has latex tubes in some species, e.g., 
G. afrlcanuui (122) and G. Gnernon (119). 
Oleo-resin or mucilage canals occur in a still larger number of 
families. The use of such canals by climbing plants or giant herbs 
for the translocation of food materials easily and quickly along 
stems where the cross section of the phloem is small compared 
with the size of the plant and the length of stem is just what might 
be expected. The writer, therefore, suggests that the development 
of the oleo-resin canals into a laticiferous system is part of the 
response to environment (epharmonic variation) which produces a 
climbing plant from an erect one. Such an advantageous character 
