Fungus of Loltuin. 27o 



Thriving on the nutriment obtained from these cells, and also on 

 ihat obtained from the carpellary wall, it increases tremendously 

 in amount, invading and attacking every portion of this tissue. 

 (Plate XXII. Fig. 1.) This figure represents the hyphae massed 

 together in thie area. For the most part it is difficult to discern 

 the outlines of the disorganising cells, except at the edge of the 

 ovule, wliere they are still intact, although, unlike the previous 

 .stage, the hyphae have spread now into these outer layers. The 

 nuclei of the cells of the nucellus persist for some little time after 

 inva.sion, but they become enlarged, and stain uniforndy, as shown 

 in the figure. 



The type of branching of the hyphae is very characteristic. (Plate 

 XXII. Fig. 2.) The branches are given off almost at right angles to 

 the main thread, and at their point of origin a slight swelling 

 generally occurs. They are strongly septate, and rich in proto- 

 plasmic contents, and they show numerous vacuoles and well marked 

 nuclei. If the sections are stained only with gentian violet, fol- 

 lowed by Gram's iodine solution, the majority of the hyphae in 

 these regions stain deeply, but the colourless portions noticed both 

 in the adult grain and in the ovary prior to fertilisation are still 

 present. In order to stain these segments sections at this stage 

 were subjected to congo red, after staining in the above manner. 

 Such, treatment made the study of the endosperm much simpler. 



The embryo-sac as a result of the stimulus of fertilisation has 

 enlarged considerably, the enlargement being accompanied by the 

 appearance of endosperm. The formation of this tissue is at first 

 most active at the proximal end of the sac, in the vicinity of the 

 ovum. On the dorsal proximal surface it forms a complete plate of 

 tissue, the distal extremities of which are separate and considerably 

 narrowed. These dip towards the ventral surface, and in section 

 appear as two bands of tissue, from one to two cells in width, each 

 being surrounded by nucellus. 



The cells of which the endosperm is composed are highly proto- 

 plasmic, and contain large nuclei. Starch has not, as yet, been 

 laid down in tliem. The endosperm is formed at first by a process 

 of free cell formation. This soon ceases, and further growth takes 

 place by the repeated division of the outer layer of cells, and thus 

 the tissue grows, and gradually assumes its mature condition. 

 This mode of growth is more easily followe<l at a later stage, so fur- 

 ther reference will be made to it when dealing with Stage C. 



