406 Vegetable PJiusiology. 



membrane, as is observ^ed in old seeds which have become 

 " greasy." 



Examples of cells containing fixed oils are afforded by many 

 well-known seeds, such as linseed (fig. 4), seeds of popples, cotton, 

 castor-oil, many palms, &c., in the " endosperm " or substance 

 formed to nourish the embryo ; and in rape, nuts, almonds, &c., 

 in the cotyledons of the embryo itself. It is a point deserving 

 especial remark, that starch occurs in these same structures 

 before they are completely developed, and vanishes subsequently. 

 We observe in the lower Alg<Te, again, that the starch of the 

 vegetative cells is replaced by drops of oil in what are called the 

 " resting-spores," — the reproductive cells capable of bearing 

 drought or winter-cold without losing their vitality, which in 

 these plants represent the seeds of the Flowering plants. 



Comparatively little is known at present regarding the produc- 

 tion of these fatty matters ; undoubtedly tliey are nearly related 

 in their origin to starch, from Avliich they differ in composition 

 chiefly in the diminution of the proportion of oxygen. A certain 

 proportion of oily matter occurs very generally in structures 

 abounding in starch, such as potatoes, or with starch and " soft " 

 cellulose, as in beans and pease, where it is apparently sus- 

 pended in the albuminous protoplasm. Possibly a portion of the 

 fat given in analyses of the green parts of plants, as of grass 

 (and dried as hay), may be derived from the chlorophyll. 



Dextrine and sugar are substances of universal occurrence in 

 plants, but, being excessively soluble, they are generally found only 

 as constituents of the watery cell-sap, invisible to the microscopist, 

 and only to be discovered by ordinary chemical examination of the 

 juices ; yet they are really among the most important of the pro- 

 ducts of the cell ; and their formation and their transformations, 

 in company with starch, cellulose, and the other substances 

 devoid of nitrogen, constitute some of the principal operations of 

 healthy vegetation. 



We have seen above that starch-granules are converted into 

 dextrine by heat, sulphuric acid, and other agents. This con- 

 version occurs in the cells of starchy seeds in germination, as is 

 seen in malted barlc}-. Since, therefore, we find dextrine in the 

 expressed juices of the organs of plants which are in a state of 

 active vegetation or development, while it is replaced in a great 

 measure by starch, cellulose, or fixed oils in resting organs, we 

 cannot avoid the conclusion that dextrine constitutes one of the 

 transitory, soluble forms of the neutral ternary series of com- 

 pounds (cellulose, starch, &c.) holding the assimilated food in a 

 condition in which it is directly apjjlic able for organisation through 

 the medium of the albuminous formative matter. 



The various sugars — grape-sugar, cane-sugar, &c. — stand in 



