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A TEXTBOOK OF THEORETICAL BOTANY 



AECIDIOSPORE 



INTERCALARY 

 CELL 



Fig. 292. — Pticcinio graminis. A, Development of the aecidial hyphae in the base of 

 the aecidial cup. B, Development and abstriction of aecidiospore. The aecidio- 

 spore is binucleate. {After Allen.) 



As in the Barberry leaf the myceHum in wheat is chiefly intercellular. 

 Only minute haustoria enter the cells. All this mycelium is diploid, in 

 the sense that each cell contains a pair of nuclei which regularly divide 

 together and are termed conjugate nuclei or, more briefly, a dicaryon 

 (Fig. 294). After a few days the mycelium begins to form sori (Fig. 295) of 

 yellow, binucleate spores called uredospores, which burst through the 

 leaf epidermis in lines, which are from a few millimetres to several centi- 

 metres long. These spores are produced in the summer (Fig. 293) and are 

 only able to reinfect other grass plants. They are oval in shape and have a 

 warty cell-wall (Fig. 296). Towards the end of summer there appears 

 among the uredospores another kind of spore of a dark-brown colour, the 

 teleutospore (Fig. 297). These increase in numbers until by late autumn 

 they have replaced the uredospores entirely (Fig. 298). Teleutospores are 

 smooth-walled and spindle-shaped. Each divides transversely into two 

 cells. In each cell are two nuclei which fuse when the spore is mature. 

 Thus we see that the conjugate nuclei, which came together at the formation 

 of the aecidium, do not fuse until the production of the teleutospores. The 

 teleutospores when shed may lie upon the ground for some time, and do 

 not usually germinate until the spring. Each cell has a germination pore 

 in its wall, and from this grows out a short hypha. Into this there passes the 

 fused nucleus from the cell of the teleutospore. This nucleus divides twice, 



