4 BOTANICAL GAZETTE [JULY 
of the trial host possessing a suberized cortex the seeds are sown 
only on the first to the sixth year’s growth. It has already been 
demonstrated that infection will not normally take place on older 
tissues.? It has been experimentally proven, however, that by 
scraping away the dead surface tissues of the bark on parts of 
branches as old as 7 years, and which still contain chlorophyll, it 
may be possible to secure infection. The number of seeds sown 
on each trial host has been maintained at 20 for greenhouse cultures 
and, owing to possible accident to the seed, so for outdoor work. 
It seemed desirable to try to maintain the seed at a fixed number so 
that the relative susceptibility of all trial hosts to any one form of 
mistletoe may be compared. Because it is impossible, especially of 
cultures in the open, to know that all seeds sown remained on the 
trees, the relative susceptibility of all trial hosts was further tested 
in most cases where it was particularly desirable to do so and 
whenever it was possible, by using a fixed number of trees of any 
one genus. A record of the source of seed of all trial hosts and of the 
place where the trees were grown was kept. This seemed desirable 
in view of the question of influence on the morphology of the 
parasite. In the case of transplants the trees had not been trans- 
planted very long to the place where cultures were made. The 
seeds demand a period of rest before germination, and if stored 
under cool and moist conditions may be carried over and sown in the 
spring. Sowings as late as April have resulted in successful 
inoculations. The low temperatures of winter also seem beneficial 
to the seed, as it is observed that a higher percentage of seeds 
germinate which have undergone freezing temperatures. This 
probably accounts for the greater number of positive results 
obtained in outdoor cultures. If the seeds are stored in warm, 
dry air, they lose their vitality very rapidly, owing to the evapora- 
tion of moisture from the chlorophyllaceous endosperm. Germina- 
tion tests show that the seeds are capable of germination some 2 
weeks before they are normally expelled from the capsule, so that 
it has been possible to sow the seeds of some species early in Sep- 
tember. Care must be taken in sowing seeds on Larix before 
2 WEIR, J. R., Mistletoe injury to conifers in the Northwest. U.S. Dept. Agric. 
Bull. 360. p. 8. 1916. 
