HISTOLOGY OF PHLOEM IN WOODY ANGIOSPERMS 
375 
3. Phloem of one-year-old twigs from mature trees has many of 
the characteristics found in the phloem of seedlings. 
4. There is no gradual advance in sieve-tube type from type i to 
type 3 which parallels our present ideas of phylogeny. 
5. All types of sieve tubes are present in the woody dicotyledons, 
the so-called "herbaceous type," with single transverse sieve plates, 
being probably about as frequent as any other. 
6. Widely different types of sieve tubes are found in the woody 
species of the same family and sometimes even within the woody 
species of the same genus. 
7. Companion cells are present in all families of the woody dicoty- 
ledons studied, although usually in smaller numbers than ill the 
phylogenetically higher forms. 
8. The sieve tubes of the lower woody dicotyledons are fundamen- 
tally different from those of the gymnosperms and vascular crypto- 
gams. 
9. There is little correlation between type of vessel and type of 
sieve tube. 
The writer wishes to acknowledge his indebtedness to Dr. A. J. 
Eames, of Cornell University, under whose direction the work was 
carried on, and to Professor I. W. Bailey, of the Bussey Institution, 
Harvard University, for assistance in the use of photographic apparatus 
at his laboratory. 
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5. Hemenway, Ansel F. Studies on the phloem of the dicotyledons. I. Phloem 
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6. Hemenway, Ansel F. Studies on the phloem of the dicotyledons. II. The 
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