STRUCTURE. 61 



more or less cubical or rhombohedral crystals of calcium oxalate embedded 

 in the wall. Schenck (1884) states that the completed crystals are formed 

 on the inside of the primary walls of the cell, followed in the usual way 

 by deposits of layers of secondary thickening. Kohl (1889) and Arcangeli 

 (1890, a) support this view, in opposition to Molisch (1882) who thought 

 the crystals were only partly embedded in the wall, and to Van Tieghem 

 (Traite de Bot., 12 ed., p. 644-5) wno considers them to be simply incrus- 

 tations and not crystals at all. That they are truly embedded is shown 

 by the fact that a protuberance still remains after the salt is dissolved out 

 by acid. Kohl (1. c.) gives a copious list of plants in which such " ter- 

 tiary " calcium oxalate is found. Idioblasts are derived from ordinary 

 young parenchyma cells ; these become distended on one or more sides 

 into the air-canals or smaller intercellular spaces. In a narrow canal, 

 the further extension of the cell takes place in two directions, resulting 

 in a long, double-pointed (bipolar) idioblast, attached somewhere on one 

 side. This type is very plentiful all through the petioles of the Eu- 

 castalia species ; a row of such iclioblasts occurs in these petioles next 

 to or near the epidermis ; a similar row was seen in N. .-atizibaricnsis 

 and in a hybrid of this near the leaf, but in no other species were they 

 observed. If a cell bears two such elongated outgrowths, its shape 

 resembles a long narrow H. But where the future idioblast lies next to a 

 broad air-canal, it usually puts out several arms in different directions, 

 giving the well-known stellate form ; all possible shapes from the simple 

 two-pointed fiber to a star with 8 or more arms may be found. These 

 have been frequently observed and figured heretofore. They vary in 

 number at different levels in the petiole. Thus, in N. tubcrosa, near the 

 rhizome the marginal ring of bipolar idioblasts numbered about 18, near 

 the middle of the same petiole 100, near the leaf 60 ; in N. odorata there 

 were none at the rhizome, 60 to 70 midway, and 100 near the leaf; N. 

 zanzibariensis X had about too near the leaf. A comparison of the num- 

 ber of idioblasts of all kinds in different species was made by counting 

 those visible in a single field of the microscope (Leitz, oc. 2, obj. 3) at 

 the center of the petiole (between the four main air-canals) ; the results 

 are shown in the subjoined table. The varieties of N. odorata, viz, minor, 

 rosea, and N. e.vqiiisifa Hort., are like the type in this respect. N'. flava 

 and mcxicana agree in having no bipolar idioblasts, but many small, short- 

 armed, stellate cells in the canals. 



In addition to idioblasts, there are found rather plentifully (one every 

 6 to 15 cm.) in the air-canals of petioles (and peduncles) of Apocarpiae, 



