homologous Alternation of Generations in Plants . 359 
examples. Mucor has frequently been referred to as showing 
an alternation, and it has been pointed out how from the 
zygospore one or more thick hyphal tubes are formed, which are 
non-sexual, and at once form gonidiophores ; that the mycelia 
derived from these gonidia may again propagate by gonidia, 
until finally a formation of zygospores may take place. In 
such a life-cycle an homologous alternation of potential 
gametophytes 1 is to be seen, similar in its main aspects to 
that in Vaucheria , the gonidia being examples of gameto- 
phytic budding, not a true spore-formation such as that in 
Ferns or Mosses. It is further to be noted in support of this 
that while in Mucor the hyphae which germinate from the 
zygospore are non-sexual, in Sporodinia they may directly 
produce fresh zygospores 2 . 
Brefeld 3 has discussed the dependence of the Mucorini, as 
also of Fungi at large, upon changes of external condition, as 
regards the formation of sexual and non-sexual organs of 
reproduction : he has pointed out that where sexual and non- 
sexual modes of reproduction occur on the same individual, 
external conditions may take part in determining the pre- 
ponderance of the one or the other : starving may encourage 
sexuality, while high feeding encourages non-sexual repro- 
duction ; but he points out that in certain forms sexuality 
has so far fallen into abeyance, that suitable external con- 
ditions are insufficient to induce it with certainty; but this 
point, which is applicable for large families of Fungi (and, as 
he shows, to the Mucorini themselves), need not interfere with 
the general conclusion that in these organisms also the alter- 
nating modes of reproduction are to be viewed as originally 
the outcome of alternating external conditions, and not as in 
any sense absolutely fixed stages. Other reasons may have 
supervened to make one stage or the other more prominent 
in the life-cycle of a given species or family 4 , or even lead to 
1 Vines’ Lectures, p. 634. 2 De Bary, Fungi, p. 147. 
3 Schimmelpilze, Heft IV, 1881, p. 74. 
4 With regard to the abeyance of sexuality in Fungi, compare Marshall Ward, 
Q. J. M. S., 1884, pp. 305, & c . 
