LOSS OF WATER 243 



Bleeding. — Bleeding, which was first investigated by Hales 



(1735), is the flow of water and cell sap with the included materials 



from cut and wounded plants. It is thus not a process which 



takes place under normal and healthy conditions. The amount 



of material which exudes differs with the plant, with the time of 



year, etc. The following table, taken from the work of Eckerson 



(1908), shows some of these variations: 



Mean quantity Days of Mean pressure in 

 Liant £ n c c ji ow atmospheres 



Begonia coccinea 168 29 0.858 



Chrysanthemum frutescens 40 15 1.014 



Fuchsia speciosa 99 23 1.24 6 



Helianthus annuus 30 16 1.276 



Ly coper sicum esculentum 13 5 1.164 



Pelargonium zonale 15.5 10 0.881 



In some plants, such as the sugar maple, the southern pine, the 

 rubber tree, and the Mexican agave, the bleeding is of great com- 

 mercial importance. In these cases the exudate is collected and 

 from it are obtained maple sugar, turpentine, rubber, and pulque. 

 In the case of the maple, 3-7 liters may be derived from a tree each 

 day during the sugar season; while the agave of Mexico and 

 Central America may furnish 500 liters of sap during the season! 

 After the plant has grown for ten to twenty years it sends up a 

 huge flower stalk bearing many flowers and fruits, but just as 

 this stalk is about to develop the bud is removed. Into the hol- 

 low thus formed the plant exudes 7-8 liters of sap a day for about 

 two months. The record daily amount thus far reported is from 

 the wine palm of Malasia (Caryota) which is reported to exude as 

 much as 50 liters a day! Although this individual flow is excep- 

 tional, it has been calculated that from an acre of these trees 

 about 14,000 gallons of exudate may be collected annually. 



The conditions under which bleeding occurs are an abundant 

 water supply and a limited normal loss by transpiration. The 

 spring, when there is abundant water in the soil and the leaves 

 are not yet developed, is hence the ideal season for such bleeding. 

 This explains also why the removal of the top of the plant results 

 in bleeding; the water supply is maintained below and the normal 

 outlet above is removed. The amount of sap thus exuded may be 

 far greater than the total volume of the roots, showing that water 

 continues to enter the plant after the wound or cut has been made. 

 A sunflower (Helianthus) bled 5,830 c. c. of liquid, while the total 

 volume of the roots was only 3,370 c. c. 



