Nutrition of Plants. 161 



The probability is that green saprophytes take carbon from 

 their substratum in a form unfitted for the manufacture of cellu- 

 lose and other carbohydrates, whilst those that are not green 

 must obtain carbon in the form of a compound, the direct ab- 

 sorption of which could be dispensed with if chlorophyll were 

 present. 



There is no well-marked boundary line between plants which 

 absorb organic compounds and those which absorb inorganic 

 compounds from their respective substrata ; and there un- 

 doubtedly exist plants capable of taking up botla kinds of material 

 at the same time. 



It is not a matter of indifference to these plants at what 

 temperature and in what state of the air in respect of moisture 

 the decomposition of humus takes place. Many plants live 

 only a short time in a garden, even though the earth in which 

 they are embedded be removed with them, owing probably to 

 some difference in the organic compounds formed under the 

 altered conditions. Saprophytes are much more fastidious as 

 regards the quality of their nutriment than one might expect. 

 A large number are associated with the decaying remains of par- 

 ticular plants and animals only. 



A number of plants exhibit contrivances which obviously have 

 for their object the capture and retention of such small creatures 

 as may fly or creep on to their leaves, and it has been ascer- 

 tained by searching experiments that the majority of these plants 

 use the animals they capture, in one way or another, as sources 

 of nutriment. For the most part the animals caught are insects, 

 ■ and the term insectivorous or carnivorous has been applied to 

 the class in question. About 500 are known. The most ex- 

 tensive group is that of the bladderworts. Their capturing 

 apparatus consists of little bladders with orifices closed by a 

 valve, which permit objects to penetrate into the bladder, but 

 not to issue out of it. They are rootless plants which live sus- 

 pended in the water, and, according to the season of the year, 

 either sink down to the bottom or ascend to just below the sur- 

 face. The animals, mostly minute crustaceans, such as water- 

 fleas, after entering the bladder, perish after a short time, decay, 

 and the products of their decomposition are sucked up by special 

 absorption-cells developed within the bladder. 



In the pitcher-plants some of the leaves are converted into 

 pit-falls, and the escape of the captured prey prevented by a 

 number of points lining the inner wall of the cavity, and directed 

 from the aperture towards the closed bottom. They are of 

 various shapes — tubular, funnel-shaped, straight, bowed like 

 sickles, or spirally twisted. Among these is the well-known 

 side-saddle plant of America. 



In another group of carnivorous plants are forms with scale- 



