312
LIONEL F. JAFFE
by the eggs and has a molecular weight of the order of 10
s or more. Perhaps this substance is rhizin, but my own guess is that this low-flow
agent is some relatively immobile precursor of rhizin. Two discrepancies
suggest that it is not rhizin. First, the observed correlation of the positive
group effect (Fig. 12) seems to imply that rhizin gradients are a link in
the amplification process which render polarity irreversible. Yet flow is
most effective before 4 hours, whereas irreversibility does not begin until
about 12 hours after fertilization (Fig. 6). Second, if cells are grown upon
nylon screens, it is possible to force medium through this substratum and,
thus, between interacting cell pairs. A cross-flow as rapid as 2 ju/second
scarcely affects the positive group effect (Neuscheler and Jaffe, unpublished data). This flow independence would appear to be incompatible
with a rhizin mobility of less than 10~
6 cm
2
/second.
4. Thallus
Effects
Kniep (1907) observed that Fucus eggs will germinate toward pieces
of the adult plant. Eggs of one Fucus species responded to thalli of
another. A figure of the effect shows it extending a few tenths of a millimeter from the thallus.
I have begun to re-examine this phenomenon. The effect shows no
specificity whatsoever: The eggs show a strong tendency to germinate
towards thalli of all the dozen marine plants successfully tested. These
included six diverse brown algae, five diverse reds, and one marine
angiosperm, Phyllospadix.
In the cases of at least one brown alga
(Egregia),
one red (Iridophycus)
as well as Phyllospadix,
the effect was
still half-maximal (i.e., 75% germination toward the thallus), 5 mm
away (Figures 5 and 14).
Orientation toward Fucus thalli is markedly increased by illumination
(of both thallus and eggs) with red light
3 strong enough to support
photosynthesis; it is also increased if the source of attractant is wrapped
in a dialyzing membrane.
These facts indicate that the universal attractant is a relatively small
molecule. This is indicated not only by its traversal of the dialysis membrane but also by its diffusing more than 5 mm in 18 hours or less (for
this yields a diffusion constant of the order of 10~
5 cm
2 /second).
Also the data suggest that this "attractant" is one which is destroyed
by an egg secretion; otherwise it is very difficult to understand how the
requisite gradients could be established. If the concentration profile of
3
Red light does not orient the eggs directly.
LIONEL F. JAFFE
by the eggs and has a molecular weight of the order of 10
s or more. Perhaps this substance is rhizin, but my own guess is that this low-flow
agent is some relatively immobile precursor of rhizin. Two discrepancies
suggest that it is not rhizin. First, the observed correlation of the positive
group effect (Fig. 12) seems to imply that rhizin gradients are a link in
the amplification process which render polarity irreversible. Yet flow is
most effective before 4 hours, whereas irreversibility does not begin until
about 12 hours after fertilization (Fig. 6). Second, if cells are grown upon
nylon screens, it is possible to force medium through this substratum and,
thus, between interacting cell pairs. A cross-flow as rapid as 2 ju/second
scarcely affects the positive group effect (Neuscheler and Jaffe, unpublished data). This flow independence would appear to be incompatible
with a rhizin mobility of less than 10~
6 cm
2
/second.
4. Thallus
Effects
Kniep (1907) observed that Fucus eggs will germinate toward pieces
of the adult plant. Eggs of one Fucus species responded to thalli of
another. A figure of the effect shows it extending a few tenths of a millimeter from the thallus.
I have begun to re-examine this phenomenon. The effect shows no
specificity whatsoever: The eggs show a strong tendency to germinate
towards thalli of all the dozen marine plants successfully tested. These
included six diverse brown algae, five diverse reds, and one marine
angiosperm, Phyllospadix.
In the cases of at least one brown alga
(Egregia),
one red (Iridophycus)
as well as Phyllospadix,
the effect was
still half-maximal (i.e., 75% germination toward the thallus), 5 mm
away (Figures 5 and 14).
Orientation toward Fucus thalli is markedly increased by illumination
(of both thallus and eggs) with red light
3 strong enough to support
photosynthesis; it is also increased if the source of attractant is wrapped
in a dialyzing membrane.
These facts indicate that the universal attractant is a relatively small
molecule. This is indicated not only by its traversal of the dialysis membrane but also by its diffusing more than 5 mm in 18 hours or less (for
this yields a diffusion constant of the order of 10~
5 cm
2 /second).
Also the data suggest that this "attractant" is one which is destroyed
by an egg secretion; otherwise it is very difficult to understand how the
requisite gradients could be established. If the concentration profile of
3
Red light does not orient the eggs directly.