CELL SIZE AND SURVIVAL IN CONIFER CAMBIUM

Abstract

The pseudotransverse divisions of fusiform initials by which the cambium of conifers is accommodated to increasing girth tend to occur at relatively high rates of frequency. The overproduction of new initials is accompanied by extensive cell loss. The continuation or reduction of fusiform initials after origin in anticlinal division is evidently related to cell length and extent of ray contacts. The largest fusiform initials generally survive and repeat the cycle of elongation and multiplication by pseudotransverse division. The cells of intermediate length continue or fail in varying proportions, the rate of failure tending to rise with increasing frequency of anticlinal division. As a rule the initials with the largest area of ray contacts persist and those with sparse ray contacts decline. The shortest fusiform initials are usually lost, passing off into maturation or undergoing further diminution to ray initials. The continued selection of the longest of the newly formed fusiform initials, which is operative at all stages in tree growth, undoubtedly contributes to the maintenance of an efficient cell length in the secondary vascular tissues.