91 



tree is not a menace in a community but the tree is doomed once 

 the main trunk is invaded. We hope that pruning has saved 

 the one or two infected pines of this vicinity. Infection is most 

 generally through the leaves or the bases of the leaf clusters. 

 In mature trees it may be some years before the cambium, the 

 growing layer of the trunk, is reached and killed by the fungus 

 but seedling trees are quickly girdled and killed. (18) 



The pitch pine is host to several rusts, each one with a dif- 

 ferent alternate host. From New Jersey southward there is a 

 species which shifts to oak. Around Norton in May, I have 

 found on needles of the pitch pine the tiny projections of 

 aecidia of Peridermium acicolum. In the fall any clump of 

 goldenrod may show the bright yellow clusters of its uredo and 

 teleutospores on the under-leaf surfaces. (45) In the fall also 

 one finds on leaves of sweetfern the slender, brown, hair-like 

 clusters of teleutospores of Peridermium comptoniae. The 

 aecidial stage of this rust deforms the pitch pine host; it causes 

 a fusiform swelling of the main stem of young trees. (56) 



These tree rusts have taken us far afield but if we walk again 

 through college grounds we may add to our list two more rusts 

 of double hosts. In May the elder bushes are in full foliage and 

 both leaves and stems are swollen with a rust infection. x\rthur 

 in 1902 linked the elder rust with a teleutosporic stage on one 

 of the sedges. His description of his preliminary guesses and 

 his methods of vertification give incidentally a glimpse of a 

 man with an absorbing interest. (7) 



The fields in May are whitened by blossoming Houstonias. 

 At close range one may distinguish among them clumps where 

 the flowers stand taller than their neighbors and where the 

 leaves have lost all green color. Such plants are found to be 

 literally covered with eruptions of spermatia and aecidia; even 

 the calyx of the flowers shows the infection. The rust here has 

 much the same effect as has the absence of light upon plants. 

 Lacking light a plant does not build chlorophyll and therefore 

 cannot build sugars. The botanist calls this condition etiolation 

 and explains: "An etiolated plant is growing to death at the 

 expense of what organic carbon compounds it possessed at the 

 beginning." (6) In the case of the rusted Houstonias the para- 

 site is the cause of the etiolation yet in other respects this 

 parasite shows the usual restraint and adaptation of a rust to 



