406 



HOT A N V 



I'AIIT II 



described above. 



and a lower fertile cell (/>'), hut the fertile cells fuse in pairs with one another. 

 the upper i>ortions of tin- separating walls breaking down (C). The two nuclei lie 

 side by side and divide simultaneously (conjugate division. Two of the daughtei- 

 miclei remain in the lower part and two pass to the upper portion of the dividing 

 cell, and this upper portion is separated hy a transverse wall as the first spoiv- 

 mother-cell (/>). In other respects the formation of the secidiospores proceeds as 

 A iwridium is not formed in Plirmjiiiiilni.m. 



The ripe, hinucleate ;ecidiospores (Fig. 3f>l 

 D) arc shed and infect a new host plant. Kadi 

 spore gives rise to an intercellular mycelium 

 which soon proceeds in the summer to hear uredo- 

 spores or summer spores. These appear in small 

 circular or linear groups and arise singly from 

 the enlarging terminal cells of the hyplue (Fig. 

 348, 5, 6). They have two nuclei like all the cell- 

 of the mycelium developed from the secidiospore. 

 They serve commonly to ensure the spread of the 

 fungus in the summer. Later, either in the same 

 or in distinct sori the teleutospores are formed. 

 and in these the fusion of the two nuclei to a 

 single one takes place ; such a fusion as a rule is 

 found to take place in the young basidium. 



The two types of cell-fusion in the formation 

 of the recidium are also found in other Uredineae, 

 and must be regarded as replacing a formerly 

 existing method of fertilisation. If we attempt 

 to derive the Uredineae from the Ascomycetes 

 the spermatia must be regarded as now function- 

 less male cells, and the so-called fertile cells in 

 the young secidium as corresponding to carpo- 

 gonia. Extending the comparison further the 

 mycelium proceeding from the fecidiospore in the 



Uredineae and the nredospores and teleutospores 

 , ., ... ,, , . ,. ,. 



sterile cell ; , fertile cells ; at <* bonle n lt > to g ether wlth the basldia > formed 

 tli.- ]>;.ssage of a nucleus from the by the latter, would together correspond to the 

 adjoining cell is seen ; B, formation asexual generation (sporophyte) of the Asco- 

 of the first spore-mother-cell sm, niyce tes The basidiospores would thus correspond 



FIG. 351. Phrngmiilium riolaeeum. 

 portion of a young tecidium 



which from i the first iecidios^re from the basidiospore would be equivalent to the 

 () and the intercalary cell (z) have sexual generation (gametophyte). 

 arisen ; smo, the second spore-mother- flie life-history of the Rust-fungi is thus a 

 B^cRMA^r WCidiOSI> rP ' (Am>F complicated one. The several forms of spore may 



appear in the course of the year on the one host. 



such Uredineae being termed autxecious. On the other hand the spermogonia and 

 jecidia may occur on one species of host plant, and the uredospores and teleutosiKjrcs 

 on another, often unrelated, plant. In these hetercecious species there is thus an 

 alternation of host plants ( 77 ). 



An example of an hetercecious Rust-Fungus is afforded by Pweiltia pnMRMlM, 

 the rust of wheat. It develops its uredospores and teleutospores on all the green 

 parts of Gramineae, especially of Rye, Wheat, Barley and Oats. The a>cidia and 

 spermogonia of this species are found on the leaves of the Barberry 



