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. 



63. 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. 



64. 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 theLactucaceae, 

 Papaveraceae, etc., as well as in a few 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. 



(6) 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. 



