128 BOTANICAL GAZETTE [February 



of perforations in the sieve tube walls. The protoplasmic masses 

 are connected by delicate strands which penetrate these perfora- 

 tions (figs. 7, 8). 



The general tendency in the modification of sieve tubes from 

 the lower to the higher vascular plants is toward an increasingly 

 smaller number of sieve plates. First, there is a decrease in the 

 number of walls upon which the plates occur. In some ferns each 

 sieve tube wall contiguous with the wall of a similar cell bears 

 sieve plates, while in most angiosperms they occur on the terminal 

 walls only. Again, there is a tendency toward diminution in the 

 number of plates on a given surface. In ferns (5, p. 180) there are 

 several rows of plates, or they may be closely crowded together; 

 in Vitis there are a number of elongated plates on the oblique 

 septae; in cucurbits there is a single plate. In Keteleeria the 

 occurrence is limited to the walls seen in radial sections and the 

 oblique terminal walls. This is true of gymnosperms in so far as 

 the records are available. The plates are arranged in a single 

 interrupted series of groups. In this respect Keteleeria is much 

 more advanced than Encephalartos (5, p. 181, fig. 78); the latter 

 has plate groups closely distributed over the radial faces. More- 

 over, the plate groups are much less numerous- on the radial faces 

 in Keteleeria than on the oblique terminal faces. This is a further 

 advance toward the condition in angiosperms. It seems probable 

 that the investigation of other forms in this respect would give 

 valuable evidence with reference to genetic relationships. 



Embryo. — The embryo of Keteleeria is of considerable morpho- 

 logical interest; it throws light upon the polycotyledonous embryo 

 of Coniferales, and also the meristem of the primary root shows 

 characters heretofore unknown among gymnosperms (2, 7, 8, 9, 10). 

 Pirotta (16) has described the seedling. 



In the embryo, as found in the mature seed, the following 

 regions occur: cotyledons, leaf bud, and primary root. Beginning 

 at the exterior, a cross-section of the root, taken near the central 

 region (figs. 24, 25), shows the coleorhiza, the cortex, the region of 

 meristematic cells and mucilage cells, and the central axis. 



There is a cotyledonary tube which extends throughout approx- 

 imately two-thirds of the length of the embryo. The cotyledons 



