TRICHOGYNE HYPOTHESIS 21 



From a comparison of all these observations it now becomes 

 certain that, in the Uredinales, the typical mode by which the 

 binucleate condition arises is by the conjugation of two similar 

 cells, each provided with a large nucleus and an abundant 

 supply of food. This fusion-cell can afterwards branch by the 

 formation of lateral buds, usually in basipetal succession, and 

 may thus produce several rows of spores at once ; by a similar 

 branching bunches of uredospores and teleutospores can arise in 

 the sori of those spore-forms (Blackman, '06, Christman, '07, 

 Dittschlag, 10, Hoffmann, 11). See Figs. 37, 156. 



At first, it may be supposed, the two conjugating cells 

 belonged to a definite basal layer or spore-bed, as in P/irag- 

 midium, Puccinia spp., and Melampsora Rostrupii ; but after- 

 wards they ceased to be arranged in a layer, and conjugation 

 took place between two purely vegetative cells in the mycelium 

 beneath. The beginnings of this change are seen in M. 

 Rostrupii, and its final product in such wn'cro-forms as P. 

 Adoxae where the greater part of the mycelium has synkarya. 



Whether the upper sterile cell which is so frequently met 

 with is to be considered as an abortive trichogyne is not so 

 certain. But it may be remarked that, since the sori generally 

 arise beneath the epidermis, no fertilisation could have taken 

 place by non-motile spermatia unless there were something of 

 the nature of a trichogyne to protrude through a stoma. In 

 this connection it is important to remember that in Uredinopsis, 

 one of the lowest of the Uredinales, the sori of primary uredo- 

 spores, i.e. secidiospores, seem always to arise beneath a stoma ; 

 other sori can arise in many genera in the same way, and in 

 the genus Hemileia the pedicels of the uredospores protrude 

 into the air through the stomatal pore. Moreover we know 

 that, while secidia of the enclosed higher types, as in P. Caricis, 

 arise at some depth in the host-tissues, and the basal layer and 

 its peridium are covered by a considerable thickness of dead 

 empty cells (which are afterwards pushed to the sides), the 

 secidia of the more primitive form, the cseoma type, are shallow 

 and are not enclosed in a peridium, but are either quite naked 

 or surrounded only by a few paraphyses. 



In the typical Uredinales, the conjugation of the two 



