48 MISSOURI BOTANICAL GARDEN. 
the hyphae had passed through the walls. The threads 
show no preference for the pits. The holes often have the 
shape of a figure 8, i. e. they enlarge within the secondary 
lamella, a feature which is common to wood destroyed by 
many wood-destroying fungi. The scarcity of mycelium is 
striking, resembling in this respect wood in which Poly- 
porus sulphureus has been growing.* In branches where 
the disease is in its youngest stage, the mycelium occurs 
more plentifully in those areas, which correspond to the 
holes to be formed later on. Between these areas the 
hyphae pass, boring through the tangential walls. 
Besides the colorless mycelium, a mycelium is often 
present in the wood between the decayed holes. This 
appears to belong to some saprophyte, which has nothing 
to do with the original decomposition. This mycelium is 
composed of brown threads which pass through the tan- 
gential walls preferably and follow the direction of the 
tracheids up and down. These hyphae form marked at- 
tachment organs when boring through the cell-walls. Frankt 
described such organs as formed by the germ tubes of Fusi- 
cladium tremulae. The hypha when it touches the epidermis 
forms a swelling with one or more pores, from which fine 
tubes push through the walls into the epidermal cells. He 
called the swollen parts ‘‘ Appressorien’’ or attachment 
organs, and believed that they aided the hypha in punctur- 
ing the wall. De Bary { found similar organs in germ tubes 
of Peziza Sclerotiorum; these were formed ‘+ owing to a 
mechanical stimulus, which the resistance of a solid body 
exerts on the hyphal branches.’’ Biisgen § described the 
* Hartig, R. Zersetzungserscheinungen des Holzes 110. 
+ Frank, B. Uber einige neue u. weniger bekannte Pflanzenkrank- 
heiten. (Ber. d. deut. bot. Ges. 1330. 1883.) 
t De Bary, A. Uber einige Sclerotinien u. Sclerotienkrankheiten. 
(Bot. Zeit. 443377. 1886.) 
§ Bisgen, M. Uber einige Eigenschaften der Keimlinge parasitische 
Pilze. (Bot. Zg. 51:53. 1893.) 
26 
