4 Raymond J. Pool 



give way to the perithecia containing ascospores (Plate I, figs. 

 11-12) which are more resistent to the unfavorable conditions 

 which obtain at the final death of the host or with the approach 

 of leaf fall and the assumption of the resting state by the host. 



De Bary first worked out the history of the development of the 

 perithecium. At the point of contact of two hyphae a lateral 

 branch is formed on each hypha, each of which is soon cut off 

 from its mother hypha by a septum (Plate I, fig. 4) ; or the two 

 branches are formed by the tips of two adjacent hyphae which 

 come in contact and from the tip of each the septum cuts off 

 a cell. One of these branches or lateral cells gradually enlarges 

 until it is oval-oblong in shape, and becomes the oogone (Plate 

 Ij fig"- 5)- The other branch lengthens and becomes closely fixed 

 to the wall of the oogone (Plate I, fig. 5) curving over so that 

 its apex lies on the tip of the oogone. A cell is then cut off 

 from the upper extremity of the smaller branch (Plate I, fig. 6) 

 which becomes this antherid. 



The common wall between oogone and antherid soon becomes 

 dissolved and the nucleus of the antherid passes into the oogone 

 and there fuses with the nucleus of that cell (Plate I, fig. 7). 

 This conjugation marks the beginning of the development of 

 the perithecium. In fact at about this time the development of 

 the walls of the future perithecium begins. From the stalk cell 

 of the fertilized oogone (the carpogone) branches grow upward 

 and closely inclose the carpogone with a single layer of cells 

 (Plate I, fig. 8). After the stalk cell has enlarged somewhat a 

 second layer of cells (Plate I, fig. 9) interior to the first layer is 

 added to the covering of the carpogone. By copious branching 

 and intertwining the hyphae of both series become grown to- 

 gether forming a well-defined pseudoparenchymatous tissue of 

 several layers in thickness about the young perithecium. The 

 outer layers of cells become flattened (Plate I, fig. 11), lose their 

 protoplasmic contents, become brown or nearly black in some 

 cases and constitute the outer wall of the perithecium. The cells 

 of the inner layer remain soft and eventually most of them dis- 

 appear during the formation of the ascus or the asci. 



62 



