86 THE SAPROLEGNIACE^ OF THE UNITED STATES, 



mitece has been known heretofore to bear them, and their peculiarities in the single 

 form in which these have been seen will be discussed in connection with the descrip- 

 tion of that species (AiJod. completa). The special office of these organs is the ]3ro- 

 duction of bodies which, like the chlamydospores above described, may in some cases 

 germinate at once, but ordinarily constitute a resting condition of the fungus. The 

 conditions most favorable to the development of the sexual organs are not yet fully 

 understood, and the readiness with which they are produced varies much with the 

 species. The species of Saprolegnia, for instance, produce their sexual organs less 

 freely and less certainly in cultures than do those of Achlya. 



The sexual organs are produced, like the spoiangia, from the main hyphse or 

 from branches, and are commonly terminal, though sometimes intercalary, in position. 

 The female organ, the oogonium, develops as a swelling of the thread which bears it, 

 which may be termed, when not a primary filament, the obgortial hrancJi. The swell- 

 ing increases as the protoplasm accumulates, until its definite form is reached. If 

 the oogonium be terminal, its form is most commonly globular (Figs. 52, 71), though 

 often with a cylindrical basal portion (Fig. 43), and sometimes ellipsoidal (Figs. 87, 

 99). When the extreme tip of the hypha is not involved in the swelling, it forms an 

 apiculus to the oogonium (Figs. 27, 57). Intercalary oogonia are oftenest barrel- 

 shaped (Fig. 59). After the form and size of the oogonium has been determined, it 

 is separated from its hypha by a transverse wall, or, if it be intercalary, b}" two such 

 walls. The formation of the walls is characterized by the same phenomena which 

 are observed when the basal wall of the sporangium is formed. The wall of the 

 oogonium has meanwhile been thickening by the deposit of new material upon its 

 inner surface. In the simplest cases this deposit takes place evenly, producing a 

 smooth wall of equal thickness throughout (Fig. 81). A somewhat less even deposit 

 produces a roughened inner surface (Fig, 77) ; or the thickening may be wholly lack- 

 ing on certain definite areas more or less numerously scattered over the wall of the 

 oogonium, causing the pitting of the membrane which is a constant and characteristic 

 feature of certain species (Figs. 43, 72). Instead of presenting a smooth outer sur- 

 face, the whole membrane may be, from a very early stage, raised at intervals into 

 outgrowths of varying height and fi-cquency, giving it a warty or spiny appearance 

 (Figs. 55, 104). 



While the membranes of the vegetative filaments and of the sporangia always 

 give the charactei'istic cellulose reaction with chloroiodide of zinc, those of the fully 

 developed oogonia take with this reagent "=' a beautiful Indian-red shade, showing that 



*This wiis prepared by dissolving Griibler's solid cliloroiodidc of zinc in its own weight of water, or some .vhat 

 less, and then adding metallic iodine until the di sired sherry-brown color was obtained. 



