54 



HUTCHINSON'S POPULAR BOTANY 



having been cut in the bark of one of these trees with an 

 axe, " in a minute the 'rich sap was running out in great 

 quantities. It was collected in a basin, diluted with water, 

 strained, and brought up at tea-time and at breakfast 

 next morning. The peculiar flavour of the milk seemed 

 rather to improve the quality of the tea, and gave it as 

 good a colour as rich cream ; in coffee it is equally good." 



Travellers would .doubtless be thankful if the milk-saps 

 of all plants were as nutritious as the milk-sap of the 

 American Cow-tree ; but it has been otherwise ordained. 

 Some, as we have already remarked, are 'extremely injurious. 

 The latex of the famous Javan Upas-tree (Antiaris toxi- 

 FIG. 81. RAPHIDES carlo) is a deadly poison, and will produce large blisters 

 OF A SPECIES OF and painful ulcers on the person who incautiously touches 

 FUCHSIA. ^. j n the j u i ce o f the Mandioc-root (Manihot utilissima) 

 from which the tapioca of our shops is prepared the 

 Indian of Guiana dips his arrows to poison them ; and the juice of a South 

 African Spurge (Euphorbia caput-medusce) is used by the natives of Be- 

 chuanaland for the same purpose. 



Sugar, inulin, and starch are largely used by the 

 protoplasm in the formation of cellulose for the cell-walls 

 in young plants ; as are also the fixed or fatty oils olive, 

 rape, poppy, palm, etc. (see p. 58) which swim, in the cell- 

 sap in the form of minute, shining yellow globules. These 

 plastic substances all originating in protoplasm are 

 stored up as reserve material in the cells of seeds, bulbs, 

 FIG. 82. CYSTO- etc., though each has to undergo various changes before 

 tlie final conversion into cellulose is effected. Chief among 

 these changes is their transformation into the soluble sub- 

 stance glucose, or grape-sugar, already mentioned, which 

 is conveyed through certain conducting cells to that part of the plant where 

 new cells are being formed. How admirable is the wisdom directing this 

 complicated process ! Had the glucose been deposited in 

 the first instance, it must have undergone fermentation, 

 and thus would have become worthless before the plant 

 was ready to make use of it ; but the deposition of starch 

 (or its equivalent), which can remain unchanged for almost 

 any length of time, and which can at any moment be con- 

 verted into sugar, secures the desired object in the most 

 effectual manner. 



The process is known as 'metabolism (Greek metabole, a 

 changing) a term which is very comprehensive. It in- 

 cludes, indeed, not only all the chemical changes which 



. , ' . , . -, , , n ,,. , 



take place in the protoplasm, but the resulting phenomena 



FIG. 83. CYSTO- 

 LITH. 



Crystals in a cell of Wal- 

 ,_nut-tree (Juglans regid). 



