40 THE TISSUES OF PLANTS 
the laticiferous tubes. The walls are lined with cyto- 
plasm containing nuclei. They are mostly thin but in 
Euphorbia the walls are thick and elastic. 
53. Two distinct types of laticiferous tissue may be 
‘ distinguished: (1) Non-anastomosing and (2) Anastomos- 
ing. The former consists of branching tubes which 
originated from single cells in the embryo. These cells 
elongate and branch, keeping pace with the growth of the 
plant, forcing their way between the meristem cells 
exactly as if they were part of a fungus instead of a tissue 
of the plant in which they occur. They appear never to 
anastomose. They are found in the Euphorbiaceae, 
Moraceae, Apocynaceae, etc., i.e. in the chief rubber- 
producing families. 
54. The anastomosing milk vessels are formed by 
the fusion (that is through the resorption of the separat- 
ing walls) of adjacent meristem cells in such a way as to 
form a network of latex-bearing tubes. Short lateral out- 
growths may also be sent out from one tube to another, 
thus increasing the number of anastomoses. Laticiferous 
tissue of this type is found especially in the Lactucaceae, 
Papaveraceae, etc., as well asin afew of the Euphorbiaceae, 
e.g. Manihot and Hevea, both rubber-producing trees of 
great economic value. 
Laboratory Studies. (a) Make a thin longitudinal section 
of the stem of garden balsam (Impatiens) or any other her- 
baceous plant that has not begun to become thickened and 
woody. The section should pass through one of the vascular 
bundles. There will be found various types of tracheary 
tissue, those facing the interior of the stem being usually of the 
annular or spiral type, with reticulated and pitted types to- 
ward the outside. 
(b) Good plants for study are Tradescantia, especially for 
ringed and spiral types of tracheary tissue; Sida, for good spiral 
and reticulated types; Indian corn, pumpkin or squash, etc., © 
for large pitted vessels. 
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