40 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



hyphae which bear them. Both oogones and chlamydospores may be 

 either terminal or intercalary. 



The normal hyphae are large, varying from 3 to 7 [/. and sometimes 

 more in diameter. T}^pical hyphae, showing the false septa developed 

 at the boundary of the protoplasm and the portions of the hyphae 

 which have been evacuated in the extension of the younger parts, are 

 shown in Plate I, figure 1. At points at which the ends of hyphae come 

 in contact with the glass of the culture dish, peculiar contact swell- 

 ings are produced (PL I, figs. 5 to 7), much the shape and size of 

 antheridia, but not walled off from the adjacent hyphae and having 

 no apparent significance in the life history of the fungus. These are 

 not always terminal (PI. I, fig. 8). It is noteworthy that Hesse de- 

 scribed contact swellings at the tips of the hyphae just before pene- 

 trating the epidermis of Camelina sativa. 



The asexual nonsporangial fruiting bodies of Pythium debaryanum 

 are referred to as chlamydospores rather than as conidia, though in 

 most of the previous literature the latter term has been used for 

 them. Hesse called the terminal bodies conidia and the intercalary, 

 gemmae (74). It is believed that the best terminology and the one 

 which should be followed for all fungi, as it now is for most, is that 

 which limits the term conidium to a spore which is adapted primarily 

 for aerial distribution or which is at least readily separated as soon 

 as it is mature from the parent hypha from which it arises. The 

 most typical conidium, in fact, is a spore which is abstricted by the 

 parent hypha at maturity. The asexual spores of this Pythium re- 

 main attached to the parent hyphae indefinitely even after the hyphae 

 are dead and empty. It is a common thing to find numbers of these 

 bodies in water cultures, still attached to hyphae which are so com- 

 pletely empty that it is only with favorable lighting that their thin 

 colorless walls can be seen. So firm is the attachment that vigorous 

 shaking is required to release any considerable proportion of the 

 spores. It seems probable that in nature the spores are released 

 chiefly as a result of the destruction of the hyphae walls by bacteria. 

 While there is reason to think that Pythium debaryanum is some- 

 times disseminated by wind, it is by no means certain that it is 

 through the medium of these spores. It is true that these bodies have 

 thinner walls than are commonly found in chlamydospores of some 

 other fungi, but they have somewhat thickened Avails as compared 

 with the vegetative hyphae, and they are commonly intercalary. 

 These facts, and the indications that they are better able to with- 

 stand unfavorable conditions than are the hyphae, all tend to entitle 

 them to rank as chlamydospores. De Bary (5) speaks of them as 

 " dauerconidia." Their ability to stand drying is not entirely demon- 

 strated, but is indicated by the relative longevity of the fungus on 

 different media. On beef agar and on rice, on which no spores are 



