The Influence of Mature Tissue 2

Observations have been made on rates of increase in total numberof cells and on rates of division in isolated pea roots grownin sterile conditions in one series over a period of 9 daysand in another started from tips of different lengths. It isshown that when cultures are started from tips of 6.0 mm. excisedfrom germinated seeds the rate of increase in cell numbers increaseswith time until the fifth day and then decreases to the ninthday. It is further shown that when cultures are started fromtips of 3.0, 6.0, and 10.0 mm., the initial lag phase is longer,the peak rate in division occurs later, and the peak value tendsto be greater the shorter the initial tip. These observationsare taken to indicate that division in the meristem dependspartly on the synthesis of appropriate metabolites in the meristemand partly on a supply of metabolites from mature regions ofthe root.