76 SCIENCE PROGRESS 



without analogy, as conifers and perhaps some American 

 species of evergreen oaks produce " double " annual rings, 

 while certain trees, the oak, for instance, emit a second crop of 

 leafy shoots — the lammas shoots. 



The periodicity revealed in the production of the annual 

 ring is known to be innate. Annual rings are most marked in 

 deciduous species and sometimes distinct in evergreen species 

 (as in many conifers and some oaks) ; where they are unrecog- 

 nisable the species is evergreen. So far as is known the seasons 

 of production of the annual ring and the new leaves, both in 

 deciduous dicotyledons and evergreen conifers, fall at the same 

 time of the year, though the cycles of these two forms of 

 morphogenous activity appear to coincide neither in exact 

 times of initiation, conclusion nor phase. The close association 

 of the two processes is exemplified by an interesting observation 

 made by J. Carruthers or Holtermann on a chocolate-tree which 

 was between j\ and y\ years old. In each year of its existence 

 the treelet lost its leaves and acquired new ones three times ; 

 and when cut down the main stem showed at its base twenty-two 

 "annual " rings. Yet in cold-temperate regions the production 

 of a second crop of leaves in the one vegetative season, either on 

 the lammas shoots or after complete defoliation, does not neces- 

 sarily involve the production of a second " annual" ring, though 

 in some cases such a doubling of the annual ring ensues. Hence 

 it must be of interest to learn what relation subsists in the 

 tropics between the seasons of leaf-production and stem-thicken- 

 ing, especially in connection with evergreen trees growing in 

 the perennially moist forests. When one of these latter trees 

 has branches or large boughs that differ as regards the time of 

 the year during which they produce new leaves, two possibilities 

 present themselves. Either there may be a definite time (which 

 may extend throughout the whole) of the year during which the 

 trunk and branches thicken ; or when each branch produces 

 new leaves its cambium may become active, so that the cambium 

 in different branches would be active at different times of the 

 year. The consequence of the latter mode of thickening might 

 be that the activity of the cambium would then extend down 

 from the branch to the parent axis, perhaps affecting only that 

 side on which the branch is inserted. The result of such a mode 

 of growth would be the deposit of new wood in the form not of 

 rings but of arcs, and in the cross section of the trunk or large 



