56 BOTANICAL GAZETTE [JULY 
no reason why it should not become independent of the thallus 
body which produced it, as the leafy gametophore of mosses 
becomes independent of the protonema. The great difference 
in the final result in the two, cases arises from the fact that in 
mosses the protonema is without gametes or spores ; while in the 
case we are supposing the thallus body produces gametes, and 
the leafy axis spores. That a thallus body can directly produce 
just such a leafy axis bearing spores is testified to by the numer 
ous cases of apogamy observed among pteridophytes. In fact, 
the theoretical life history we have been tracing is concretely 
represented by the life history of a fern in which apogamy has 
occurred. 
If the phenomenon of apogamy represents the primitive 
status of the leafy sporoyhyte, it remains to imagine how this 
spore-bearing leafy axis could have become the usual product of 
the oospore. We find no trouble in believing that the usual 00s 
pore product frequently appears apogamously, for this has been 
demonstrated; but to imagine a general primitive apogamous habit 
of origin gradually passing into a predominant oospore habit of 
origin is difficult. In the condition supposed, namely, a thallus 
body producing gametes, and a special leafy axis bearing spores; 
7ygotes and spores would have the same power, the germinatiot 
of each resulting first in the thallus body and afterwards the 
leafy axis. If real alternation can be brought about by such a 
condition, the thallus portion of the zygote product and the 
_ leafy axis portion of the Spore product must be gradually elimi- 
nated. In other words, the tendency would be to eliminate that 
particular region which is.concerned in producing the reproduc 
tive body. Perhaps such a tendency is no more difficult © — 
understand than the fact that a spore produces a gametophyt€ 
rather than a sporophyte, and a zygote produces a sporophyte — 
rather than a gametophyte. A common explanation has been 
that a zygote, for some reason, stops reproducing the plant body 
Which organizes it, and beg; irely new 
structure, which certainly seems to have been the case in the 
formation of the Sporogonia of bryophytes. It would seem 1° 
