Sexual Organs of Phytophtkora erythroseptica , Pethyb. 12 7 
other Fungi. There is no fundamental difference between the penetration 
process in P. erythroseptica and the phenomenon of the well-developed 
receptive papilla in Albugo Portulacae or that of the fertilization tube in 
any Oomycete. All three are cases of two parts of the same thallus in 
close contact, one of which pushes into the other: in the one case, pushing 
well in but not piercing any wall (receptive papilla); in another, piercing 
one wall but not the opposite one (fertilization tube); in the last, piercing 
both walls and growing through (oogonial incept). It is probable that all 
three are due to differences in turgor rendered evident by a protrusion 
through a part of the wall weakened by enzymic action. At all events 
there is some evidence to show that receptive papillae and fertilization 
tubes are only expressions of differential pressures. 
He terothallism . 
The fact that the sexual organs are always borne on separate hyphae, 1 
at least so far a*s they can be traced, led to the idea that perhaps the 
Fungus was heterothallic (cf. Clinton, 9 and 10 ). Careful investigation, 
however, proved this surmise to be incorrect. A brief survey of the 
experiment will present a few points of interest. Conidia were not avail¬ 
able, so single-hypha cultures were made. The medium used was oat- 
extract agar, which has the double advantage of being clear and of giving 
a less vigorous growth. Considerable difficulty was experienced in sepa¬ 
rating the hyphae, and special methods had to be resorted to. The tips 
of the hyphae when cut off (they had to be very short as a rule) usually 
died. If a set plate of oat-extract agar be inoculated in the centre and 
an annular strip of the medium well outside the limits of growth be 
removed, individual hyphae here and there will cross the clear space and 
give rise to a good growth in the medium outside. This process was 
regulated under microscopic control, and if the hyphae were too close 
superfluous ones were removed with the point of a sterile needle. But 
this was often unnecessary, the hyphae which crossed the open space 
being far apart. 
Before this simple method was discovered individual hyphae were 
led across the empty space in very fine sterile glass tubes filled by 
capillarity with oat-extract agar. The method works occasionally, but it 
1 The condition which Dastur (13) found in P. parasitica , which also has amphigynous 
antheridia, where the oogonium is said to arise as a sort of proliferation of the basal wall of the 
antheridium, is not present here. The connexion between the stalk of the female organ and a hypha 
can always be seen in properly stained material, although it is sometimes difficult to make out in 
fresh preparations when the hyphae are empty, and this may have misled Dastur. The apparent 
continuity of the stalk of the oogonium and the wall of the antheridium is further heightened by the 
fact that the base of the male organ is normally invaginated by the frequently much swollen body 
outside, which has been compared to an appressorium. 
