CELL-CONTENTS AND FORMS OF CELLS. 241 



Tiliaceae, and Urticaceae. The secretion in these cells is some- 

 times visible even with the naked eye, and it is possible, on break- 

 ing the bark, to obtain the latex in the form of delicate, elastic 

 threads. These caoutchouc threads may be readily seen on break- 

 ing the bark of euonymus, and may be distinguished from bast- 

 fibers by their rfcadily dissolving in chloroform (Fig. 127). 



The milk- juice varies in color in different plants, being color- 

 less, as in oleander ; whitish, as in the Apocynaceae and Asclepiada- 

 ceae ; or yellowish, as in chelidonium, or orange-red, as in 

 sanguinaria. The latex of a number of plants is collected to form 

 a number of commercial products. Opium is the dried milk- juice 

 obtained from the capsules of Papaver somniferum. Lactucarium 

 is the dried milk-juice of Lactuca virosa and other species of 

 Lactuca. Elastica or India rubber is the prepared milk-juice ob-< 

 tained from a number of plants, the most important being the 

 Brazilian or Para rubber tree (Hevea brasiliensis) , the Central 

 American rubber tree (Castilloa elastica), the East Indian rubber 

 tree (Ficus elastlca), and the rubber vines of Africa (Landolphia 

 species). Gutta percha is the concrete juice of Palaquium Gutta 

 (Fam. Sapotaceae). 



ENZYMES OR FERMENTS. In connection with the growth of 

 the plant, there occurs a constant change in the substances which 

 comprise it. These changes are brought about largely through 

 the influence of a class of substances known as enzymes. Atten- 

 tion has been directed to the decomposition of starch with the 

 formation of sugar. This change is brought about by the secre- 

 tion in the protoplasm of an enzyme called amylase (diastase). 

 It is produced in the living cell, can be extracted from the plant, 

 and will produce the same effect upon starch grains which have 

 been separated from the cells. 



One of the interesting properties of the ferments is that in 

 comparison with the amount of ferment employed the product 

 formed through its influence is very large. Thus it is stated that 

 amylase is able to hydrolyze 10,000 times its own bulk of starch. 

 Results of this kind are considered to be due to catalytic action 

 of the ferments, i.e., their power of inducing chemical reactions 

 by their mere presence without themselves entering into the 

 products formed. The ferments require specific temperatures for 

 16 



