I 



31 



grow well in brick powder even when underlaid with a layer of 

 farmyard manure. 



IV. Violet G. Jackson. ''Anatomical Structure of the 



Roots of Barley." Annals of Botany, 1922. Vol. 

 XXXVl. pp. 21-39. 



The root system of a well-developed barley plant, whether 

 g-rown in soil or water culture, consists of two types of roots : (a) 

 a thin branched type, and (b) a thick "unbranched" type, with very 

 abundant root hairs. The present paper embodies the results 

 obtained from, an anatomical investigation of the two types. 



A branched root possesses a much thickened stele with a single 

 large axile vessel and six to eight xylem groups, all bounded by a 

 very thick-walled endodermis. In an "unbranched" root neither 

 the endodermis nor the stelar tissues are thickened, the xylem 

 groups number from twelve to sixteen, and the middle of the root 

 consists of thin-walled pith cells traversed by four to six ducts. 



The chief function of the "unbranched" roots is probably to 

 provide the plant with a plentiful supply of water and its dissolved 

 food, at the time when \igorous growth is setting in. This func- 

 tion is provided for by : — 



(a) Abundant root hairs; 



(h) An increased number of large vessels and central ducts ; 

 (c) The existence of a stele composed almost entirely of 

 thin-walled elements. 



This view receives support from the fact that these roots are 

 formed only during the early stages of the plant's vigorous growth. 

 Researches on the development of root and shoot showed that the 

 formation of "unbranched" roots had entirely ceased by time the 

 plant had finished its vegetative growth and was entering on its 

 reproductive phase. At this period of the plant's history, the 

 nitrogen and ash constituents are migrating steadily from the 

 straw into the grain, so that there is no need for a large root- 

 absorbing area. On the other hand, if the "unbranched" roots 

 functioned chiefly as buttress-roots, the plant would need thern 

 even more when the heavy grain is being formed ; but that is just 

 the time when their development ceases. Therefore the most 

 probable function for the "unbranched" roots is to ensure a good 

 supply of water, etc., when the plant is in a condition of strong 

 vegetative growth. 



V. Katherine Warington. ''The Effect of Boric Acid and 



Borax on the Broad Bean and certain other Plants/' 

 Annals of Botany, 1923. Vol. XXXVII. pp. 1-44. 



Boron appears to have some special function in the nutrition 

 and development of the broad bean, as this plant fails to grow 

 satisfactorily in nutritive solution from which boron is withheld. 

 The results of the experimental work are: — 



1. — In water culture a continual supply of boric acid appears 

 to be essential to the healthy growth of the broad bean plant, 

 concentrations of one part of boric acid (HgBO^) in 12,500,000 

 parts — 25,000 parts of nutrient solution being beneficial. 



In its absence, death occurs in a characteristic manner, the 

 apex of the shoot becoming withered and blackened. The addi- 

 tion of boric acid after these symptoms have set in, but before 



