r2i6 A TEXT-BOOK OF BOTANY. 



rounded projections which gradually elongate and become more 

 and more abundant and intricate. If this process be allowed to 

 take place in a test-tube or other vessel that can be shaken, the 

 water becomes turbid through the dispersion of the delicate 

 microscopic myelin protrusions, and in course of time a uniform 

 emulsion of the lecithin in water is obtained, which consists of fine 

 swollen particles. This is a colloidal solution that can be filtered 

 without change. It is not coagulated by heat, nor precipitated by 

 salts of monobasic or tribasic metals. 



Wax. — The epidermal layer of the plant shows a number of 

 modifications. It usually consists of an inner layer of cellulose 

 and an outer covering of cutin. While some of the lamellae be- 

 neath the cutin may be modified to mucilage or oil, the surface 

 of the cutin layer may have deposited upon it a coating of wax. 

 Frequently the wax is in such small quantities that it is not ob- 

 served until the sections are heated to a temperature of 90° to 

 100° C, when the wax separates in the form of oily globules. 

 According to De Bary, there are four principal forms of wax- 

 coatings. 



I. It occurs in the form of minute rods or needles, such as are 

 found constituting the bloom of fruits as the grape and plum, 

 and the stems and leaves of Eucalyptus Globulus, Ricinus com- 

 munis, etc. 2. The most common form is a simple, granular 

 coating consisting of isolated grains which may lie together as a 

 single layer. These are found in the fruits of some of the 

 Cruciferse, Iris pallida, etc. 3. The coating may consist of 

 minute rods which may be more or less bent or curled, standing 

 perpendicularly on the cuticle, as in the sugar cane, canna, banana 

 plant, etc. 4. The wax incrustation may occur in the form of 

 membrane-like layers, varying from thin scales, as in Taxus 

 baccafa, Portulaca oleracea, and various cacti, to thick layers 

 showing a striation and stratification similar to that found in 

 thick-walled cells, as in the fruit of Myrica, leaves of the wax 

 ^3\m {C eroxylon andicolum). According to Wiesner, the deposit 

 of wax is often crystalline, appearing in four-sided prisms. (Con- 

 sult A. deBary, " Comparative Anatomy of the Organs of 

 Vegetation.") 



Physiology of' Fats. — It is stated that in the photosynthetic 



