444 BOTANICAL GAZETTE [ DECEMBER 
position where they may, under the very best conditions, ger- 
minate and infect the young needles. 
For several years the time of the appearance of the spores 
and young leaves has been watched, and in every case a most 
remarkable similarity in dates has been observed. If the leaves 
are late or early in coming out the spores will be correspond- 
ingly late or early. This is exceedingly important in the econ- 
omy of the fungus, for it has been proved by successive infections 
that a difference of but two days in the age of the leaf will 
enable it to resist the fungus. Infection, in other words, must 
take place when the parts of the needles are from 0.33 to 0.66% 
long (fig. 19 a, too old; 4, proper age), otherwise the cortical 
region will be developed to such an extent that the germ tubes 
from the sporidia cannot force their way through.” 
The needles are infected wholly by means of the germ tubes 
boring through the cortical tissue before the stereomatic, thick- 
walled cells have formed. These tubes make their way to the 
mesophyll region, where they immediately begin to lengthen, in 
eight or ten days assuming all the characteristics of the mycelium 
already described. The orifice, however, through which the 
germ tube enters the leaf, soon disappears, leaving no trace of 
the manner in which the fungus reaches the mesophyll region. 
In about three months, or by the middle of August, the fungus 
has developed to such an extent that its presence may be deter- 
mined by the condition of the tips of the needles. Pale yellow- 
ish spots may be seen at these parts, and microscopic examina- 
tion of the tissue reveals the mycelium growing in all directions 
between the cells of the mesophyll region. As the season 
advances the spots or bands become more prominent, and by the 
middle of November, or even earlier, pustules, indicating the 
formation of sori, begin to appear. By the first of April, or ten 
*° For the sake of brevity the details of the experiments are omitted. Briefly ‘ z 
this case one hundred pine branches were bagged with paper bags, the work being 
carried on for two successive years. From time to time a bag was removed and the 
young leaves received a small drop of water containing germinating sporidia, after 
which the leaves were marked and the bag replaced. About 75 per cent. of the moc 
ulations made when the leaves were the proper age were successful. 
