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CHAPTER IV. 



^CIDIOSPORES. 



The mycelium originated in the tissues of the host-plant 

 by the entrance of the germ-tube from a promycelial spore, 

 after it has produced a certain number of spermogonia, 

 proceeds in the course of its development to give rise to 

 the jecidiospores. This spore-form is of considerable 

 interest, not only on account of the manner in which it 

 arises, but also by reason of its attractive appearance in 

 the mature state. The first appearance of the aecidiospores 

 consists in the formation of the receptacle (pseudoperidium) 

 in which they are contained. The mycelium destined to 

 give rise to an aecidium becomes more frequently branched 

 and interwoven. At certain points, not immediately 

 beneath the epidermis, but pretty deeply placed in the 

 parenchyma of the plant, the mycelial hyphae compact 

 themselves into spherical bodies, which at first are not 

 larger than the parenchymatous cells of the host-plant. The 

 bodies (the primordia of De Bary) gradually increase in 

 size by the addition of fresh hyphae from the mycelium. It 

 can soon be observed that the interior and bulk of these 

 bodies consist of a cellular structure, and that they bear 

 the greatest possible resemblance to perithecia (Plate II. 

 Fig. i). They are globose, but rather flattened upon their 

 upper surface — that is, the surface nearest to the epidermis. 



