-^70 Et.ltel McLennan .- 



While these changes ano proeeeding in the carpel wall, the hyphae 

 in the developing ovule are not quiescent. Ihey keep pace with the 

 growth of the ovuLe, and until the embryo-sac is at the 8-celled stage 

 they simply run between the cells of the nucellus, ramifying in 

 ever}' direction. They exten<l right through the nuciellar tissue 



^completely surrounding the end>ryo-sac. Freeman, when discuss- 

 ing the ovary of Lol/ian femulenfu in at this stage, states that hyphae 

 are comjiletely wanting on the outer dorsal surface towards the 

 embryo-sac end, stopping at about tlie level of the antipodal group. 

 If this is so, it is difficult to see how hyphae come to be present in 

 this position in tlie mature grain. As far as I have observed they 



.are uniforndy distrilnited through the inner layers of tlie nucellus, 

 Init do not generally extend into the very outer layers until later 

 in development. The dual staining properties are sliown by these 

 hyphae, but the great majority of them will pick up thie purple 

 stain. 



The first indication of any change in the relation between the 

 fungus and the cells of the ovule at this stage is the tendency for 

 tlie hyphae to form knots (Plate XXI. Fig. •'}). These ai'e especiallv 

 striking if the sections are cut rather thicker than those to be used 

 for detailed high power examination. Hanausek described the 

 occurrence of knots (Kniiuel) in the ovary of Darnel, and figured 

 them. I liave been unable to o])tain his original paper, only 



.■al)stracts withtnit figui'es being availaljle. He offered the occur- 

 rence of these knots as evidence in favour of the fungus being 

 related to tlie (^stihufi neae . Freeman says : " I have found no 



;such knotting of hyphae to indicate the commencement of Ustilagine 



rspore formation." These knots undoubtedly do occur, but are 

 rather to be regarded as the first stages in the penetration of the 

 nucellus cells. The hyphae arch round all sides of the cell before 

 entering it, and as they generally invade two or three adjacent 



•cells simultaneously, this arching gives the knot-like formations 

 above described. 1 do not think they afford any clue to the actual 

 systematic position of the fungus in question. Since they are just 

 on the point of attacking a cell th^y ore rich in ferments and 

 always stain vividly. 



Cells showinof a later stage of invasion are also ])resK.'nt in sucli 

 an ovule. Lateral branches ari.se from these enfolding hyphae, 

 which penetrate the cell wall and pass into the substance of 

 the cell itself. It soon becomes filled with a dense network of 

 •threads, and in this condition forms a most striking part of the 



