326 Harper.—Sexual Reproduction in Pyronema 
be sure whether the given structures are male cells or 
vegetative spores. Brefeld and his pupil Moller (4) have 
endeavoured to overthrow the evidence for sexuality in the 
Lichens by laborious culture experiments intended to show 
that cells which have been claimed to be spermatia in many 
cases will really germinate, and may, under especial conditions 
of nutrition, produce rudimentary thalli. Moller describes the 
germination and growth of the supposed spermatia of species 
of Buellia , Opegrapha , Graphis, Arthonia , and Calicium , and 
concludes that in every case they are merely conidia, and are 
capable of reproducing the fungal portion of the Lichen by 
simple germination and growth. He proposes to call the 
spermagonia pycnidia and their spores pycnoconidia. Assum¬ 
ing the substantial accuracy of the results as published, though 
they have not as yet been confirmed by other investigators, it 
is still quite possible that Moller has pushed too far that 
conception of sex-cells according to which they must be 
incapable of further development without conjugation. The 
inability to develop without conjugation is doubtless an 
acquired character in the evolution of sexual reproduction 
from original asexual methods, and it is quite possible in these 
simple forms, where the spermatia are plainly so similar to 
known vegetative spores both in their appearance and in the 
method of their production, that the capacity for independent 
growth has only been as yet partially lost, so that under 
conditions of especially rich nutrition, such as Moller's 
methods furnished, cells which are potential spermatia might 
return to an original vegetative condition. The weakness of 
such growth and the failure to achieve it in many cases should 
have considerable weight, from this standpoint, as evidence of 
the sexual nature of these spores. 
Loeb (23) has shown that such regularly sexual eggs as 
those of the Echinoderms will still segment regularly and 
form Pluteus larvae without fertilization simply as a result of 
changing the percentage of a certain salt (Mg Cl 2 ) in the sea 
water. These eggs are in nature incapable of further develop¬ 
ment without fertilization, but a relatively simple change in 
