558 



COMPARATIVE MORPHOLOGY OF FUNGI 



Sp. 



~~z~.z. 



if-sp. 



m 



The fusion cell elongates in the direction of the epidermis; its dicaryon 

 passes to the tip and divides. The fusion cell then divides, as in the 



earlier cells, into a small apical and large basal cell 

 (Fig. 374, 5, iz and bz). The basal cell elongates and 

 repeats the above process so that a chain of binucle- 

 ate cells arises; occasionally a basal cell may fork and 

 form several, similar, parallel chains; perhaps in the 

 multinucleate cells, the binucleate condition may 

 again be attained. By the increasing pressure of 

 the growing chain, the remains of the sterile cells are 

 pressed together into a formless mass. 



These binucleate cells thus cut off, are called 

 initial cells or aeciospore mother cells. After their 



; 2w.Z.; nuclei have completed a conjugate mitosis, each 



divides by septal formation into a large terminal 

 and small basal cell. The larger cell rounds up, the 

 walls become sculptured and thickened and it is 

 called an aeciospore (Fig. 374; 6, sp). The smaller 

 intercalary cell (Fig. 374, 6, zw. z.) disintegrates 

 and disappears, usually before the maturity of the 

 sorus; biologically it fulfills the function of a dis- 

 junctor, since by its degeneration, the aeciospores 

 are loosened from the chain for further dispersal. 

 Under favorable conditions, one finds in the young 

 sorus a crushed sterile cell above and a free aecio- 

 spore below (Fig. 375), then aeciospores with inter- 

 calary cells, aeciospore mother cells and, at the base, 

 binucleate basal cells in full activity. Finally the 

 375—Cronar- epidermis is ruptured by the pressure of the sorus 

 Hum ribicoia. Section an( j the aeciospores escape into the free air. 

 Sp^ci^oies^Zw^z'., In the aecidium, the fundament of the sorus is a 

 intercalary cells; M. k no t of plectenchy ma which is sunk several layers of 

 cells; a B!z, SP basad° cell, cells deep into the host tissue, in contrast to the 

 (x 560; after Colley, position of the caeoma. In Puccinia Pruni-spinosae, 



the hyphae of the upper half of the knot grow further 

 into the host tissue . The cells of the knot are isodiametric and about equal 

 in size. At the margin, a peridium of 5 to 6 layers of thick-walled cells is 

 formed. Further differentiation of the knot varies and may be classi- 

 fied under four types, represented by Puccinia Mariae-Wilsoni (P. 

 claytoniata) , Uredinopsis americana (U. mirabilis), Puccinia Violae and 

 Endophyllum Sempervivi. 



In the Puccinia Mariae-Wilsoni type, (Fromme, 1914), to which con- 

 form P. Poarum, Uromyces Poae (Blackman and Fraser, 1906), Cronartium 



-Sp. 

 -HZ 



i-az. 



Fig. 



