36 



Bulletin 125. 



portion around the minute opening collapses, so that a distinct and char- 

 acteristic saucer-sliaped depression is produced in each. 



When the interior of the perithecium is examined a condition represented 

 in Figure 14 is found. Around the outside is a wall or shell of sterile tissue, 

 formed by the coalescence of hyplial threads. Projecting from the bottom 

 of this wall, and converging toward the apex, are numerous cylindrical or 

 club-shaped sacks, the asri, each containing eight elliptical, colorless spores. 

 Each spore is divided by from five to seven cross-walls into sections, many 

 of which are further divided by walls running across the first, as represented 

 in Figure 15. The spores measure 16-22x7-8 /i. The remaining linterior 

 part of the perithecium is filled with sterile tissue. 



The spores are capable of germinating under favorable conditions and 

 reproducing the species. Numerous cultures of the ascospores were made 



during the fall of 1895. Growth takes 

 place freely in both acid and neutral 

 potato-agar. A typical culture was started 

 December 6tli. At three in the afternoon, 

 a dilution of three plates was made in 

 acidified potato-agar, and kept in a room 

 where the temperature was 70-80° F. 

 On Dec. 7th, after twenty-one hours, ger- 

 mination had begun. 



The spore first swells to several times 

 its former size through the absorption of 

 moisture. Small protrusions then appear 

 at various points, which elongate more 

 or less as germ-tubes (Fig. 15). In many 

 cases the threads, after elongating a little, 



begin to throw off conidia by constriction 

 from their apices (Fig. 16). Such threads grow no further, but continue to cast 

 off conidia in numbers. The conidia are oval in form, 4-6 // long, and closely 

 resemble those of Tubercularia, except that they are a little smaller. The 

 other germ -tubes elongate much by apical growth, and become much 

 branched, forming a compact mycelium. Branching begins quite early, but 

 septa do not become numerous until the thread has attained a considerable 

 length. No definite relation could be seen between the number of germ- 

 tubes and the number of cells of the spore. It occasionally happened that 

 two or three tubes came from one cell, while some cells put out none. 



After the mycelium was three days old, conidia in great numbers were 

 cast off from the sides of the threads, much as in the case of the Tubercularia 

 (Fig. 16). Short lateral branches are put out, which become constricted 

 when as long at> the diameter of the thread, and the apical portion is thrown 

 off as an elliptical conidium. This process may be continued indefinitely 

 by the same branch. The form of the lateral branches varies, some being 

 long and tapering, while others are short and conical. 



Innoculations were made from the plate cultures to sterili*ed bean stems by 



15. 



Germinating spores of 

 Pleonectria. 



