1916] MEINECKE: PERIDERMIUM AND CRONARTIUM 239 



FACULTATIVE HETEROECISM OF CRONARTIUM QUERCUUM 



Recent inspections of oaks of the infected area on the Monterey penin- 

 sula disclosed an apparent parallelism between the facultative nature of 

 the heteroecism of Peridermium harknessii and that of Cronartium Quer- 

 cuum. The relative scarcity of the latter in the immediate vicinity of 

 the former has already been pointed out. At the time of the first obser- 

 vation (first half of April) no Cronartium in its telial form had developed, 

 but uredinial sori were fairly common on young leaves and more frequent 

 on old green ones. The leaves of Quercus agrifolia remain living and 

 green on the tree throughout winter and often until late in spring. On 

 last year's green leaves fresh urediniospores came forth more or less 

 abundantly from the old Cronartium spots, generally in a circle im- 

 mediately around the dark-brown, dead, sunken-in places occupied last 

 year by the Cronartium. The mycelium of the fungus, therefore, evi- 

 dently overwinters in the leaf and produces urediniospores in the follow- 

 ing spring, which are able in their turn to infect the young sprouting 

 leaves. Hedgcock 23 has successfully inoculated Quercus lobata, Q. cali- 

 fornica and Castanopsis chrysophylla with urediniospores from Quercus 

 rubra. It is, of course, not impossible that some of the uredinial sori on 

 the young leaves were the results of infection from aeciospores from 

 Peridermium harknessii on Pinus radiata. The numerical relation of 

 these sori to the old ones, however, speaks for an infection through ure- 

 diniospores rather than through aeciospores from Peridermium harknessii, 

 at least early in the season. Later infection from Peridermium may be- 

 come more plentiful. Inspection of the same stands in the beginning 

 of May did not disclose an increase in sori. The sporulation (uredo) on 

 young leaves had all but stopped. No telial stage was found. The 

 old green leaves were still on the trees, but sporulation on these had 

 stopped altogether. 



The Cronartium on another evergreen oak, Quercus durata, mentioned 

 above, seems to behave in a similar manner. Here the uredinial sori 

 were not very numerous on last year's leaves and were distinctly rare 

 on this year's foliage, which was about one-third developed. The sori 

 are smaller than on Quercus agrifolia, but here again the old sori produced 

 urediniospores in quantities. The urediniospores are rather large. Oc- 

 casionally very small telial columns were found; it was impossible to decide 

 whether these were the product of last year or recently formed. 



This uredinial infection explains the occurrence of Cronartim Quercuum 

 in apparent independence of a heavy infection of Peridermium harknessii. 



The heteroecism of the Californian Cronartium Quercuum seems to 

 be facultative as is that of Peridermium harknessii on Pinus radiata. 



23 Phytopath. 1: 131. 



