MICHIGAN ACADEMY OF SCIENCE. 87 



One of the most common excretory products found in higher plants 

 is calcium oxalate, which assumes quite a variety of crystalline forms 

 varying from the needle-shai>ed bodies known as raphides, to the large 

 star-j)ointed bodies found in cactus stems. Calcium oxalate cnstals are 

 located in various places in the plant, most freciuently, in empty cells 

 of the cortex or in the neighborhood of vascular bundles in leaves. Some 

 of the largest are found in intercellular spaces as for example in 

 gladiolus bulbs where they develop so large as to be seen with the un- 

 aided eye. 



Calcium carbonate occurs occasionally in plant cells but is found 

 most frefiuently on the epidermal structures in the neighborhood of 

 water-pores. It is often so abundant as to cover a very considerable 

 area of the leaf surface around the pore. Calcium sulphate is also oc- 

 casionally found in crystalline form and often associated with calcium 

 carbonate. Many of the drug products on the market are without any 

 doubt products of excretion by the plant, but it is not the intention here 

 to go into this matter further than to mention rhe facts as they bear 

 upon the discussion of the forms of excretion in roots and leaves. It is 

 these forms of excretion to which special attention has been given and 

 concerning which data has been collected for this paper. 



Excretion from roots: The present view as to the nature of the sub- 

 stances excreted by roots may be expressed in the following quotation:^ 

 ^'The principal substances diffusing from roots are mainly COo passing 

 out as H2CO3, phosphoric, hydrochloric, sulphuric and formic acids and 

 their salts, preeminently substances which would aid the plant to ob- 

 tain needed food materials from the soil."" 



It has long been known, and it is easil}' proved, that CO. is liberated 

 from roots in the processes of growth and of vital activity, but so far 

 as I am aware, no one has ever proved definitely, or claimed to have 

 proved, that organic matter like glucose, or saccharose is excreted by 

 plant roots. Carbon dioxide is a natural product of aerobic respiration 

 and consequently it is easy to see that COo would be liberated from 

 actively growing roots, and that in very considerable quantity. But 

 it is somewhat surprising to find glucose and similar substances ex- 

 creted. To prove this is not difficult. Young seedlings when grown in 

 distilled water or upon moist filter paper give out comparatively large 

 quantities of such substances, which soon become infested by aquatic 

 or other fungi and by enormous numbers of bacteria. Intermingled with 

 this glucose material are the waste cells of the root cap which, no doubt, 

 contribute to the quantity or bulk of the excretion but which can be 

 seen as distinct from it. 



When the mass of material is heated, it gives off the odor of burning 

 sugar and later turns brown and black. If heating is carried on further, 

 then the mass is burned down to ash, which proves to be composed of 

 patassum and calcium, mainly, but may also contain other metals. This 

 syrupy mass adhering to the root tip gives a distinct alkaline reaction 

 to litmus test paper. It might be said in this connection, that litmus 

 paper usually becomes very distinctly red, when lying around the labora- 

 tory for a long time and such paper should be held over an ammonia 

 bottle until it is nearly neutral. Paper so treated shows a very quick 



^Plant Physiology, Pelrce, p. 126. 



