278 DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



of aecidia, but no spermogonia. But these may be exceptional cases connected 

 with parthenogenetic development, and would be no valid objection to the presence 

 of sexuality as a rule, if the latter is supported by other and sufficient reasons. But 

 these are at present wanting. We know of nothing in the Uredineae, which, like 

 Woronin's hypha in Xylaria, can be regarded with any probability as even a rudimentary 

 archicarp, much less therefore as a distinct female sexual organ or even carpogonium. 

 Yet it cannot be maintained with absolute certainty that there is no such organ, for we 

 are still unacquainted with the first beginnings of the hymenium with its envelope ; there 

 is a gap in the observations, and technical difficulties which are not yet overcome 

 stand in the way of the completion of our knowledge. In young groups of aecidia a 

 phenomenon is observed not unfrequently and without great difficulty, which seems to 

 be in favour of the supposition that there is an archicarp duly equipped for conception ; 

 short obtuse hyphal branches project from some of the stomata like the tips of the 

 trichogyne in Polystigma (see on page 215) and may be traced here and there to a 

 young perithecium. But the chief point, the continuity of such a possible trichogyne 

 with the supposed archicarp on the one side and on the other its distinct relation to the 

 spermatia, has not yet been shown ; there is nothing in the phenomena observed which 

 compels us to speak of trichogynes and not simply of branches of the mycelium which 

 may as well grow outwards from a stoma as in an inward direction into an inter- 

 cellular space. 



In presence of this uncertainty we cannot at present deal with the recently published 

 statements of Rathay, that the spermogonia of the Uredineae allure insects to visit 

 them by their fragrance which has long been known, by the saccharine contents 

 of the mucilage which surrounds the spermatia, and by their colour which is often 

 supplemented by the bright red or yellow tints of the part of the host where they occur, 

 and thus make them involuntary agents in the dispersion of the spermatia. 



The spores, as they may be shortly termed, which are produced in the 

 aecidium are mature and capable of germination from the moment that they are set 

 free from the hymenium, and retain their vitality for some weeks under favourable 

 circumstances. In a moist environment they put out usually from pores previously 

 formed in their wall (see page 100) thin- walled germ-tubes which receive the proto- 

 plasm of the spore-cavity together with the oily colouring matter ; each spore forms 

 as a rule only one tube. The next stages in the growth of the tubes and in connection 

 with them the general course of development in the species exhibit in the better 

 known cases two chief sets of phenomena. 



In the first case observed only in the genus Endophyllum the germ-tube, when it 

 has become about ten times longer than the diameter of the spore, ceases to lengthen 

 and assumes the characters of a promycelium (see on page in). It then 

 divides at once by transverse walls, and each of the cells thus formed, generally four 

 or five in number, with the exception usually of the lowest, sends out a short 

 subulate lateral sterigma, and on its apex abjoints a thin-walled curved ovoid spore 

 (Fig. 127). This is called a sporidium to distinguish it from other spores. Regarded 

 from another connection it belongs to the category of gonidia, if the view of the nature 

 of an aecidium with which we set out is the true one. The promycelium dies away 

 when the sporidium has been abscised. The sporidia germinate under favourable 

 conditions immediately after abscision, sending out a germ-tube which penetrates 

 through an epidermal cell into the parenchyma of the proper host, and there 

 developes into a mycelium which ultimately produces new spermogonia and 

 aecidia. This completes the life history of the plant. 



