88 TWELFTH REPORT. 



and positive alkaline reaction. Now it is not easy to see how such ex- 

 cretion could contain hydrochloric, sulphuric, formic acid, etc. It may 

 be, however, that some of these substances develop as result of bac- 

 terial decomposition in connection with the soil but in the case of a 

 medium of distilled water, and of a duration of 18 to 24 hours, there 

 is very little chance for extensive bacterial action. 



The root excretion is so constant in occurrence and reaction with 

 seedlings that the conclusion seems warranted that such excretion is a 

 normal function of roots of seedlings possessing a supply of stored 

 food. Whether this function is general with rootlets of plants past 

 the seedling stage, we are not yet prepared to say. Further investiga- 

 tion is needed. At all events, so far as we have gone, it seems to be 

 true of plants well advanced in gTOwth. but the amount of excretion is 

 much less. This is especially so Avith respect to the organic portion of 

 the excretion. 



How such a function can be of advantage to a plant is not easy to see, 

 nor is it easy to see how it can result otherwise than as a distinct loss 

 of what appears to be organized plant food. And yet. in looking closely 

 into the matter, we are led to the conclusion that such is inevitable 

 especially in seedlings. The seedling has as yet no excretory tissue, 

 no dead cells in which to store up excretion, and excretionrs are a nec- 

 essary result of the metabolism involved in groAvth. The root tip, in- 

 cludiiiig about ten or fifteen mm. from the end, is actively growing. 

 Highly organized material is being reduced and unless it be on the out- 

 side of the plant there is no place for excretions. Since the conducting 

 tissues are not yet developed, the excretions are necessarily found near 

 the place of active growth. Consequently it is not surprising after all, 

 to find organic matter located as excretion substance near the root tip 

 — the region of most active growth. 



The excretion soon becomes attacked by fungi and bacteria which 

 further reduce it, so that it becomes slightly acid, due partly to the 

 presence of carbon dioxide. The mycorrhiza fungi gain their start upon 

 the host plant here, and to such plants as are symbiouts with mycorrhiza, 

 there is no doubt that the excretion serves a purpose by furnishing a 

 nutrient medium suitable to the rapid development of fungus hyphae. 

 Such fungus hyphae finding a supply of nutritive material in solutiou 

 in connection with the loose cells near the root cap penetrate into such 

 loose tissue and remain attached to or embedded in the rootlet. Later 

 on the hyphae of the fungus absorb water and unorganized substances 

 in solution from the soil and transfer it to the host. 



Actively growing fungi excrete substances Avhich may react upon the 

 soil particles, setting free or bringing into solution useful inorganic 

 matter. Bacteria often serve a similar function and bacteria are often, 

 if not always, found in the root excreta after a day or two. Excretions 

 of bacteria' often react upon the soil and in fact, these organisms are 

 perhaps the most important agents in rendering unorganized soil ma- 

 terial into a soluble form which may then be available to plants. 



Now, the root hairs of plants are located a short distance, a few 

 centimeters, from the root tip. and as the root makes its way through 

 the soil, the root hairs follow after the tip and would therefore be in 

 a position to profit to the best advantage by any material made available 



