HISTOLOGY OF STEM OF THE WAX PLANT 265 



Schultze's solution at first changes the color to wine-purple and 

 then shows the cells that contained it to be quite filled with starch. 

 I have been unable to identify this substance with any description 

 at my command of the coloring matter of plants. It is probably 

 complex in structure, and further investigation is needed by some one 

 more skilled in micro-chemistry than myself. 



Crystals 



These are composed of oxalate of lime and are contained in con- 

 siderable numbers in this band of tissue, mostly outside of the sclerotic 

 girdle. They are of a general spherical shape, presenting many sharp 

 points over the surface as shown in pi. II, fig. 6. It has been stated ^ 

 that they are inclosed in a cellulose wall and supported by threads of 

 cellulose ; this I have been unable to confirm, but think from the way 

 in which they act when treated with hydrochloric acid or Schultze's 

 solution that it is so. They certainly have a nucleus of organic 

 matter. 



Milk Cells 



PI. I, Fig. 7 



Davids, in 1872, published a pamphlet containing the results of 

 his investigations of the milk cells of the EuphorbiacecB, Moracece, 

 Apocynacece, and AsclepiadacecB, and there gives references to the litera- 

 ture on the subject. The Apocynacece and Asclepiadacece he treats 

 together, taking Nerium oleander as the type of one, and Hoya car- 

 nosa of the other, stating that in the latter the milk cells are almost 

 exclusively confined to the parenchyma inside the sclerotic girdle. 

 He gives their diameter from 18 to 21 ^l, states that they are moder- 

 ately branched, have no septa, and that their ends are closed. Also 

 that they are formed in the growing point and are developed simul- 

 taneously in the hark and in the pith. They are not cell fusions hut cells 

 which hy stretching and branching reach a considerahle length in the 

 intercellular space. They consist of fundamental cells and are not to he 

 considered homologous with the true hast nor as part of the hundle sys- 

 tems (Gefasshiindel Systeme). They do not anastomose with each other 

 and therefore huild no " system'' in plants. As far as my investigation 

 has gone the above observations are correct, but the milk cells are 



^ Botanischer Jahresbericht, 1880, vi, p. 31. 



