Germination of Arceuthobium occidentale , 113 
«r 
cortex (unshaded) and the branches from this mass growing where medullary ray cells were before 
infection took place, m. r., unabsorbed group of medullary ray cells surrounded by the parasite 
(shaded), ph., phloem part of a vascular bundle of the pine, xyl., xylem part. c., cambium ring 
traversed by branches of the parasite growing into the wood, x 50. 
Fig. 23. Diagrammatic cross-section of a part of infected pine branch, showing continuous 
strand of tracheids (and vessels) from the wood of the host (unshaded) to a part of the parasite 
(shaded) in the cortex, c.p. , cortex. Other letters as above, x 300. 
Fig. 24. Tangential section of wood of pine showing direct contact of Arceuthobium tracheids 
(shaded) with those of pine (unshaded), x 416. 
Fig. 25. Similar tangential section, but in younger wood, showing (a) that young and forming 
Arceuthobium tracheids thicken their walls at places that correspond with the thicker parts of the 
walls of the pine-tracheids. x 450. 
Fig. 26. Cross-section of pine, showing sieve-plates in section in the walls of the sieve-tubes of 
pine, but no sieve-plates in the walls of the Arceuthobium cells directly in contact, x 900. 
Fig. 27. Tangential section through wood ( [xyl. ), cambium (£.), and phloem (ph.) of pine 
branch 1 cm. below a branch of Arceuthobium. Note the comparatively small size of the medullary 
rays, x 84. 
Fig. 28. Tangential section in same branch in the bunch of Arceuthobium. Note the great 
increase in size of the infected medullary rays the cells of which have been entirely displaced and 
absorbed by Arceuthobium cells, x 84. 
I 
