RICHARDS. — DEVELOPIMENT OF vECIDIA. 257 



For the earliest stages, pieces of tissue in which with a hand 

 lens nothing but the spermogonia could be detected wei-e taken. 

 In sections of these, the youngest stages of what De Bary called 

 " primordia" were seen, which consist of a large number of branching 

 hyphie, which are massed together and finally become compacted into 

 an irregular sized ball. Even the youngest conditions may be dis- 

 tinguished from developing spermogonia, both by the fact that they 

 are embedded more deeply in the leaf, and also because the hyphaa 

 are more loosely arranged than in a spermogonium of equal size. 

 After this massing together of the hyphte to form the primordium 

 has kept on for a certain time, changes are seen to take place. The 

 hyphoe already septate become very much more so, and the small 

 cells so formed begin to enlarge very much. The result is that a 

 large part of the primordium now consists of a pseudo-parenchyma 

 of cells of very irregular size and shape, and with walls of very vari- 

 able thickness. Finally, the whole primordium changes to this pseudo- 

 parenchyma with the exception of a weft of tightly woven hyphse 

 around the periphery, which merge at the base into a mass of some- 

 what more loosely compacted threads. A careful search was made 

 in these young stages to determine if anything in the nature of a 

 trichogyne could be found, but in all of the sections examined nothing 

 to which the function of a trichogyne could be ascribed was seen. 

 Occasional hyphse were seen protruding out of the stomata, but they 

 did not connect with any of the primordia, and showed no evidence 

 of any specialization. 



During the formation of the pseudo-parenchyma, the young a?cid- 

 ium increases very much in size, and consequently displaces the cells 

 of the host plant. The primordium, starting in a large intercellular 

 cavity, fills it, and then the hyphte, pushing out, soon surround the 

 neighboring cells, and often cut them off from their fellows. Such 

 isolated cells are usually completely broken down by the hyphaj, and 

 apparently absorbed- In this case practically no distortion accom- 

 panies the growth of the hyphge or tecidia. 



Earlier than the formation of the pseudo-parenchyma no sign is 

 seen of the hymenium, nor can the hyphae which are to form it be 

 distinguished. At about this stage, however, there arises at the base 

 of the primordium a definitely differen tilted hypha, which may in 

 respect to its further development be called the fertile or sporogenic 

 hypha. It is to be distinguished from the ordinary sterile hyphse 

 which surround it by its highly granular and somewhat more refrac- 

 tive contents. It absorbs aniline stains slowly, but to a great amount, 



VOL. XXXI. (n. s. xxiit.) 17 



