240 



A TEXT-BOOK OF BOTANY. 



are present in the Apocynaceae, Asclepiadaceae, Euphorbiaceae, 

 Aloraceae, and Urticacese. 2. Laticiferous vessels are long tubes 

 resembling the latex cells, but are formed by the absorption of the 

 transverse walls in the superimposed cells. They develop very 

 early, the cell-fusions taking place, in some instances, in the 

 primary meristems. They may be either simple or branching, the 

 branches connecting with other tubes and forming a net-work 

 These anastomosing tubes can be separated readily from the sur- 



OOO o <^ 



00 



Fig. 128. Microscopical appearance of latex in Ficus elastica, showing small globules 

 and sphero-crystals which separate soon after the removal of the fresh latex. — From a draw- 

 ing by Hogstad. 



rounding tissues by boiling the material with dilute solutions of 

 potassium hydroxide. The laticiferous vessels usually occur as- 

 sociated with the leptome, although they may be found in other 

 tissues of the axis and leaf. Milk vessels are found in the fol- 

 lowing families : Araceae, Campanulaceae, Compositse, Convol- 

 vulacese, Euphorbiaceae, Geraniaceae, Musacese, Oleaceae, and 

 Papaveraceae. 3. Secretory cells resembling laticiferous cells, 

 in that they have a latex-like content, although probably of 

 secondary origin, have been found in the Celastraceae, Oleaceae, 



