I 12 
Peirce . — The Dissemination and 
EXPLANATION OF FIGURES IN PLATES III AND IV. 
Illustrating Dr. Peirce’s paper on Arceuthobium . 
The figures were drawn either free-hand or with a Zeiss drawing-prism. 
PLATE III. 
Fig. i. Fruiting branch of Arceuthobium occidentale. Nat. size. 
Fig. a. Section of branch of Pinus radiata, showing part of mass of Arceuthobium tissue in the 
bark, the connexion of this with the wood of the pine and the aerial branch of the parasite. Nat. size. 
Fig. 3. Diagrammatic sketch of a longitudinal section of a fruit of Arceuthobium. a-b , the line 
above which the epidermis is heavily cutinized. c-d, the abscission layer, c. ep., cutinized epidermis 
with many stomata, c . p. parenchyma cells with cellulose walls and chlorophyll grains. /., the 
layer of cells with lignified walls. e.p., epidermis scarcely if at all cutinized, with no stomata, g. c., 
gelatinous collenchyma. g.f c., gelatinous fruit coat, s.f c., sclerotic fruit coat, end., endosperm. 
emb ., embryo, with radicle up. x 10. 
Fig. 4. Cross-section near middle of fruit from which the ‘ seed ’ has been discharged. Large- 
celled thin-walled parenchyma with small but many chlorophyll grains and some yellow oil-drops. 
v. b., the vascular bundles, x 29. 
Fig. 5. Epidermis from upper part of fruit, showing heavily cutinized and thick outer walls, and 
depressed guard-cells, x 300. 
Fig. 6. Part of a longitudinal section through a fruit, at the base, showing very thin-walled 
abscission layer between thick -walled tissues, x 300. 
Fig. 7. Wet * seed ’ much swollen, showing markings on the gelatinous surface and the small 
hard ungelatinized end of the ‘ seed ’ whence the radicle will emerge, x 24. 
Fig 8. Section through gelatinous outer coat of the ‘ seed,’ showing long cells with narrow 
cavities, outer part of walls gelatinized, inner cellulose (spirally thickened). Long cells attached to 
thick sclerotic cells forming continuous coat around the ‘ seed.’ x 300. 
Fig. 9. Tangential section of gelatinous coat of a ‘ seed.’ In 95 % alcohol, x 334. 
Fig. 10. Part of the same section after lying in water fifteen minutes on the slide. The swelling 
of the gelatinous outer portion of the cell is very marked, x 334. 
Fig. 11. ‘ Seed’ germinating on a pine-needle. x 3-4. 
Fig. 12. Longitudinal section of * seed,’ showing gelatinous outer coat, the sclerotic inner coat, 
the endosperm with the undifferentiated embryo at one end. The radicle is up, the cotyledons 
down and indicated only by the slight notch, x 20. 
Fig. 13. ‘Foot’ or holdfast formed by the tip of the root when it catches on rough bark. 
Longitudinal section. From the centre the infecting haustorium will penetrate the host, x 29. 
PLATE IV. 
Fig. 14. Longitudinal section of * seed ’ showing two embryos of very unequal size, x 20. 
Fig. 15. Germinating ‘seed’ on branch of pine, showing root already bent away from the light 
(negative phototropism) toward centre of the tree, x 8. 
Fig. 16. Somewhat older germinating seed with root growing away from the light, x 8. 
Fig. 17. Seedling still older, with root forming foot attaching it to the bark, x 6. 
Fig. 18. Showing the growth of the foot at the expense of food in the upper part of the seedling 
from which the coats have already fallen away, x 6. 
big. 19. Still older and larger foot ; the upper part of the seedling much shrivelled and nearly 
empty, x 6. 
Fig. 20. Aerial branches already emerging after recent infection of the branch, x 6. 
Fig. 21. Young bunch of Arceuthobium branches. Note that the ‘seed’ has not yet fallen 
away and that the pine-branch is already enlarged, x 2. 
Fig. 22. Cross-section of pine branch showing mass of Arceuthobium cells (shaded) in the 
