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by masses of tissue becoming separated from one another, — 
albumen, opium (in Pupaee somniferum), eouchaan (in a 
_Siphonia elastica, Lsonandra gutta, and species of Ficus), bone- " 
shaped grains of starch (in tropical species of Euphorbia), &c. 
The laticiferous are often distinguished from the vesicular 
vessels only by the absence of raphides. ‘Transitional forms 
- between sieve-tubes and laticiferous vessels occur appara 
in the elder and in Aceracee. | eS: 
It has not yet been certainly determined whether the latex isa ~- 
product of excretion or a reserve material. The laticiferous vessels ~ 
and the true vessels together have been compared to the venous and 
arterial blood-vessels of animals ; but since a direct connection between 
‘them has not been proved, and the mature vessels are normally filled : 
with air, this comparison cannot be maintained. 
Closely connected with the laticiferous vessels are” 
certain groups of cells, to which belong the formation and 
secretion of particular substances, and which have been — 
included under the indefinite term receptacles for sap. In — 
examining them, the chief point to notice is whether the ~ 
cells themselves contain the secretion formed in them, or — 
whether it has been transferred into the nearest intercellular 
spaces. It is not always possible, however, to draw.a sharp — 
line of demarcation between these two conditions, which “4 
may both occur together. . 
Single cells of this nature, or smaller groups of cells, — 
are called glands, while the larger sap-receptacles which ~ 
extend to a greater length through the parenchyma are 
termed fassages. These latter never possess a true cell-wall, 
and are not produced by a deliquescence of cell-walls, ae 
, 
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Acge thus forming a cavity between their cells; and are there- a 
fore true intercellular spaces. Whether this is a result of | 4 
vital processes or of pressure exercised by the separated — 
masses on those in their vicinity is not yet ool 
ve restn- pas rae as in Conifers (Figs 7 1857 
