.V.< 1 I >l A 



but the mycelium produced is very scanty. Their function 

 will be discussed in a later paragraph, but it may be mentioned 

 here that all attempts to produce infection by means of them 

 have uniformly failed. 



The iEcmiUM. 



Before the spermogones have completed their development, 

 similar but larger conglomerations of hyphse arise on the lower 

 surface of the leaf, a little way below the epidermis, which they 

 raise up into a rounded dome. These masses enclose a number 

 of erect hyphse of two kinds — an 

 outer series of parallel closely- 

 joined colourless hyphae, forming 

 the peridium, consisting of more 

 or less hexagonal cells, which meet 

 above and roof over the dome- 

 shaped cavity ; and an interior 

 series which remain shorter and 

 give off from their upper end 

 parallel chains of spores called 

 aecidiospores, which fill the whole 

 of the enclosed space. Each new 

 spore is produced beneath the older 

 ones, which are thereby pushed 

 gradually up. Finally, this struc- 

 ture, which is called an aecidium, 

 ruptures the epidermis, forces its 

 way between the cells, the peridium 

 bursts at the summit, the edges become revolute, and there is 

 formed a white cup-shaped hollow, its floor covered with erect 

 chains of orange spores (see Fig. 1). These spores have a 

 rather thin, colourless, finely warted cell-wall, and are filled 

 with rich bright-orange granular and oily contents. The 

 mycelium which forms the a?cidia is continuous with that 

 which bears the spermogones, and its cells are uninucleate, but 

 the spores themselves are binucleate. The origin and meaning 

 of this change will appear afterwards. 



1—2 



Fig. 3. Leaf of Nettle (under 

 side) showing the secidia 

 of P. Curie is on the lamina 

 and petiole, x i. 



