178 DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



The abjointed sporidia then unite in pairs in many species, either before or after 

 their separation from the promycelium. They unite by means of short transverse 

 processes, which may be placed at the point of insertion or at the apex or in the 

 middle, and form double cells, as is shown in Figs. 81, 83, 84 B. Coalescence by 

 pairs takes place also in the cases which come under No. 2 between the segment cells 

 of the promycelium. Adjacent cells unite with one another by means of short 

 processes arising near the partition-wall and forming with one another a short lateral 

 excrescence (Fig. 84 C left), through which the protoplasm of the two cells coalesces 

 after disappearance of the separating membrane. Communication is established 

 between cells which are not next neighbours by larger lateral branches, which may 

 form curved tubes or loops on a promycelium or even transverse bridges between two 

 promycelia. 



The simplest form in which the development proceeds is by the production 

 at a spot in the conjugated pair of a slender germ-tube with acropetal growth, which 

 gradually receives the whole of the protoplasm of the two cells (Fig. 83 x)\ it has 

 been shown that in many species this tube can penetrate into the phanerogamous 

 plant which is its proper host, and there develope a mycelium which produces new 

 resting-spores ; it may therefore be shortly described as an incipient mycelium or 

 mycelial primordium. 



FIG. 84. A UstilafO longisfima, Tul., germinating. B V. Tragopogonif. C U. Carbo, Tul. /> promycelium, j primary 

 sporidia. Further explanation in the text. A magn. nearly 700, B 390, C more than 390 times. 



The process is more complicated in Tilletia, in many "species of Entyloma, 

 in Tuburcinia Trientalis, and as a general rule in Urocystis Violae, where a (secondary) 

 sporidium is acrogenously abjointed on a short lateral branch from the conjugated pair 

 (Figs. 83 /, 8 1 d), which then gives rise to the incipient mycelium. 



Deviations from the above course of development occur under otherwise similar 

 conditions in individuals of the species in which this development is the almost 

 invariable rule. Firstly, the germ-tube which proceeds from the resting-spore may 

 assume the characters not of a promycelium as described above, but of an incipient 

 mycelium with acropetal growth but not producing sporidia. Secondly, the conjuga- 

 tion of sporidia of the first order in pairs may be omitted, but the sporidia may still 

 put forth tubes which are similar in conformation to the incipient mycelium ; this may 

 happen to all or to a majority of the primary sporidia of a whorl in some species, for 

 instance, of Entyloma, or, when the number of the members of a whorl is uneven, to 

 one sporidium, while the others conjugate in pairs. 



These phenomena, which are individual exceptions in the cases which we have 

 been hitherto considering, are the prevailing and even the invariable rule in another 



