4 THE FLOWERING PLANT. 



which they reduce to solution, often in a kind of external stomach 

 (e.g., pitchers of the pitcher plant). On the other hand, some 

 animals, all rather low in the scale, contain chlorophyll, and by 

 its means utilize the carbon dioxide of the air and simple salts 

 dissolved in the water around them ; and it is not unlikely that 

 animals exist which contain so much chlorophyll as to obviate 

 altogether the necessity for solid food. Some comparatively high 

 animals, such as the tapeworm, which are not green, can dispense 

 with such food in another way. They live as endo-parasites, i.e., 

 within other animals, and feed at their expense on the soluble 

 products of digestion, which, however, are by no means simple in 

 composition. This mode of life may, and often does, do away 

 with the necessity for an internal digestive cavity, as in the 

 example quoted. 



The branching form and absence of locomotor powers cease to 

 be plant-tests among many microscopic forms, which may be oval 

 or spherical, and capable of the most active locomotion. And 

 many comparatively high animals (oyster, &c.) are sedentary, 

 though their embryos swim actively about. There is no trace of 

 a nervous system in the lowest animals ; and, lastly, cellulose is 

 not exclusively a vegetable product. It is found in some few 

 animals, as, e.g., the sea-squirts (Ascidians). 



But in spite of these partial exceptions, there is no difficulty 

 whatever in distinguishing plants from animals, except in the 

 very lowest forms. These are believed to be nearer a common 

 stock from which all organisms have sprung, and are, therefore, 

 more alike than are the higher plants and animals, which have 

 diverged more or less in different directions from that stock. 



Differences between Living and Non-Living Matter. — At this 

 point the question naturally arises, " How does organic living 

 matter differ from inorganic non-living matter?" Here, so far 

 as we yet know, sharp boundary-lines can be drawn. 



(i.) 1 The elementary chemical substances, some seventy in nurn- 

 1 >er, are supposed to be ultimately made up of infinitely minute 

 particles, atoms. Even in an element, these are built up into 

 small aggregates or molecules, while the molecules forming che- 

 mical compounds are built up from more than one kind of atom, 

 and are the smallest quantities in which a compound can exist 

 as such. When a very large number of atoms enter into a mole- 

 cule, it is said to be complex, and this is characteristic of the com- 

 pounds of which organisms are composed. All plants and animals 

 are essentially made up of a jelly-like substance, known as proto- 

 plasm, the molecule of which is undoubtedly of extreme complexity. 



1 Students who have read no chemistry are strongly advised to work through 

 such a book as Roscoe's Primer. 



