354 



THE QUARTERLY REVIEW OF BIOLOGY 



of a single cell. Such instances are not 

 uncommon on roots of collards growing in 

 simple calcium nitrate solutions. In this 

 case there is just one nucleus for the cell 

 proper and for the two hairs. In some 

 cases the nucleus may move into the base 

 only and remain there in a central position. 

 In such cases as have been observed the two 

 hairs then grow at approximately the same 

 rate. Not infrequently, however, one of 

 the hairs assumes a more rapid growth 

 rate before the nucleus emerges. In this 

 instance the nucleus almost invariably 

 passes into the hair which is growing more 

 rapidly. It is then observed that the rate 

 of elongation is thereupon retarded and it 

 may even cease elongating entirely, while 



basis of the relation of the nucleus to 

 protoplasmic streaming. The proto- 

 plasm of the root hairs of many plants may 

 be seen to be in a state of circulation, 

 flowing from the cell proper along the 

 inner surface of the lateral walls, accumu- 

 lating in the dome-shaped tip, and then 

 flowing back again along another wall to 

 the cell proper. There are also commonly 

 seen currents which cut across the interior 

 of the cell apparently forming strands of 

 cytoplasm which pass through the vacu- 

 oles. There may also be one or more 

 partitions of cytoplasm which completely 

 separate one vacuole from another. In 

 these partitions the protoplasm streams 

 also. Furthermore the paths of streaming 



A 



b. c. 



Fig. i. Duplex Root Hairs Showing the Relation of the Position of the Nucleus to the Growth of the 



Two Hairs 

 The series b-b represents different stages of the same hairs 



the rate of the other hair is accelerated. 

 After this other hair has, perhaps, at- 

 tained a greater length than the one in 

 which the nucleus is located, the latter 

 has been observed to move over into the 

 hair which is now growing more rapidly 

 (fig- i). 



It thus seems that the growth rate is 

 likely to determine the position of the 

 nucleus, rather than the position of the 

 nucleus to determine the growth rate. 

 However the position of the nucleus does 

 seem to have some relation to growth rate, 

 namely to retard or stop it, rather than to 

 accelerate or start. This relation of the 

 position of the nucleus to the rate of 

 growth may be explained perhaps on the 



may be observed to be changing rather 

 rapidly. 



It is apparent that this streaming has a 

 direct relation to the transportation of 

 materials dissolved in the cytoplasm. It 

 carries, for instance, materials for growth 

 of the root hair from the cell proper to 

 the growing tip. This material is chiefly 

 no doubt some form of soluble carbohy- 

 drate, such as the sugars, or soluble 

 polysaccharids like dextrin or inulin. 

 At the apex of the hair it is changed into 

 the insoluble amyloid, which is deposited 

 in the cell wall. Whether this amyloid is 

 later transformed into the pectic bodies of 

 the outer layer of the wall or the callose 

 of the inner layer, has not yet been deter- 



