Fungus of Lolium. 2 77 



packed with reserved food, and also the walls of the aleuroiie cells 

 become thickened, showing pits or points of communication at 

 intervals. It is a well-known fact that cambial cells embarking on 

 a period of rest show considerably thickened cell walls. The thicken- 

 ings are usually removed wholly or in part, wlien such a layer 

 recommences its activities. 



If the stamens, before they ripen, are removed from a spikelet 

 and cross-pollination is also prevented, the ovary remains small, 

 but the fungus will gi-ow rapidly in the nucellus, and ultimately 

 forms a sclerotial-like mass of hyphae, occupying the main part of 

 the ovule. Freeman records this fact for Darnel, arid I have had 

 similar results with English rye grass. Since, by preventing pol- 

 lination, endosperm formation does not take place, this dense 

 growth is only to be expected, for even in a fertilised ovary the 

 fungus is parasitic on the nucellus, and for a short period tends 

 to increase in amount. The prohibiting factor is the endosperm, 

 which destroys the hyphae as fast, or faster, than they are being 

 formed, hence removal or absence of this factor favours the develop- 

 ment of the fungal organism, and the attempt towards sclerote 

 formation is the result. 



The primary tissues have been cut off in the embryo. It lias 

 elongated considerably in length at the expense of the endosperm 

 cells adjacent to it. (Plate XXV., Fig. 3). These no longer foi-m 

 a close investment to the embryo, but have disappeared at the 

 micropylar end, and the embryo now lies free in the embryo-sac. 

 The attachment of the suspensor to the microple is broken at this 

 stage. Hyphae still run in close association with the embryo, and 

 in section it shows the hyphae running in its tissues. 



Transition from Stage G to the Mature Grain. 



Extci-nally, the only changes which are evident during this tran- 

 sition are tlie elongation of the; ovary, accompanied by an increase 

 in breadth, and the development of the embryonic area, which 

 becomes more pronounced as the scutellum develops and the embryo 

 reaches maturity. 



Sections taken at ' any stage during this period show features 

 common to the earlier stages. The increase of endosperm, resulting 

 from the continued activity of its outer layer, tends to crush the 

 hyphae.^ which are ramifying in the remnants of the nucellus, into 

 a layer running round the periphery of the seed. This layer becomes 

 more pronounced as the endosperm reaches its adult size, and tills 



15a 



