366 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



that the araucarian type of wood is older than the ])iiiaeeous type. Bamian 

 (1933, 1936) studied the formation and distribution, in the Pinaceae, of verti- 

 cal resin ducts in the secondary wood, which were found always to be the ef- 

 fects of environmental influences. In the individual species the development 

 of resin tissue increases from the seedling to the adult tree, and outwards from 

 the pith in both. Jeffrey's theory of the pinelike distribution of ducts as the 

 primitive type is not supported by the fossils. A phylogenetic enlargement of 

 the response to injury is instead indicated. The identification and classification 

 of coniferous woods in general was also dealt with by Slyper (1933), Yarmo- 

 lenko (1933), Record (1934), Peirce (1936, 1937), Phillips (1941), and Gre- 

 guss (1950, 1951), and numerous special studies were carried out. Sterling 

 (1947) summarized our knowledge of the distribution of sclereids, and Buch- 

 holz and Grey (1948, 1951) investigated their distribution in the leaves of 

 Podocarpus species. 



The occurrence and condition of axillary buds were investigated by Holt- 

 husen (1940), who found that macroscopically bare leaf axils do not contain 

 any embryonic cells or meristematic tissue. Conifers with long and short shoots 

 have as a rule a bud primordium in each leaf axil on the former. The apex of 

 a short shoot of the pine is a slender, only slightly vaulted cone; the needles have 

 no axillary meristem. Doak (1935) considered Cedrus more primitive than 

 Pimis, but Flous (1936b, 1938a) denied the supposed homology of the short 

 shoots. Gaussen (1944-1952) distinguished in general between auxiblasts (rap- 

 idly growing long shoots), mesoblasts (long shoots of more tardy growth), and 

 braehyblasts (short shoots), and characterized the "short shoot" of Cedrus as 

 a mesoblast. 



In respect to the conifer foliage leaves, Gaussen (I.e.) distinguished euphylls 

 and pseudophylls, the latter identical with the adult pine needles. The poly- 

 morphy of the leaves in this genus was especially investigated by him and his 

 students, and by Doak (1935). An interesting feature in Metasequoia (Steb- 

 bins, 1948; Morley, 1948; Sterling, 1949) is the decussate phyllotaxy, with the 

 leaves of the deciduous short shoots spreading out in one plane by the rotation 

 in opposite directions of alternating nodes of the axis and a simultaneous bend- 

 ing of the leaf bases. Goebel (1932) arranged the types of conifer leaves in a 

 series: (1) forking of bundles in the cortex as well as in the lamina (Agathis) ; 

 (2) forking in the cortex only (certain arauearias) ; (3) only a single forking, 

 occurring in the cortex [Pinus) ; (4) no forking at all. Large leaves were placed 

 at the beginning, and small, narrow leaves at the end. Florin (1938-1945, 1951), 

 however, distinguished two different types of transformation by reduction of 

 primitive many-veined conifer leaves into uninerved leaves, one based on the 

 conditions in the living Araucariaceae, and the other on those in paleozoic coni- 

 fers. The latter type, which illustrates the probable evolution of the leaf in the 

 majority of conifer families, is characterized by the direct reduction of a but 

 little complicated, cruciately dichotomized telome system (syntelome) and the 

 foliarization of the single remaining mesome. The anatomy of the leaves of liv- 

 ing conifers was described in many cases, mostly for the purposes of specific 

 identification and classification. 



As regards the history of the Coniferae, Florin (1938-1945, 1951) investi- 

 gated the upper carboniferous and lower permian conifers, with special refer- 



