594 
Notes. 
Why should there be such complex alternation in the archegoniate 
phylum alone ? The Green Flagellates show an exceptional poly- 
morphism among the Protista ; and we may fairly ascribe this to the 
fact that by their holophytic nutrition, manufacturing their own food- 
stuffs, they can grow freely and multiply in the encysted state ; while 
holozoic feeders can only do so when in the free -condition. We find 
extreme cases of this polymorphism in the genus Ulothnx , where the 
forms are adapted for all sorts of substrata, differing in moisture and 
exposure ; and the reproductive modes show a tendency to similar 
polymorphism. It is from such a stock (but thalloid, not confervoid) 
that we may well suppose the Green Metaphytes to have sprung. If 
here, owing to greater permanence of the thallus that bears the 
oosphere, the zygote or product of it’s fertilization has the opportunity 
of parasitism on the parent thallus, we can easily see the possibility 
that its resolution into a brood of- spores might be delayed with the 
formation of a new colonial condition, at first parasitic on the mother 
as in Muscineae, with partial consequent sterilization of its tissues, and 
then an acquisition of independence, with the sterilization carried to 
the extent that we find in higher Archegoniates and Flowering-plants. 
As to nuclear reduction, we may attempt to ascertain its significance 
by classifying the stages at which it occurs. In Desmids, &c., it 
occurs at the first divisions of the zygote. These plants have no 
colonial tissue-formation. In Fucaceae and Metazoa, it occurs in the 
first gametogenic cell-divisions ; these have the single alternation of 
colonial and protistoid cell-multiplication ; in Archegoniata, and higher 
plants, it occurs at the inception of the sporogenic cell-divisions, the 
first resumption of protistoid cell-multiplication after the doubling of 
the number of chromosomes by fertilization. For the present I omit 
the case of the Ciliata, so exceptional from all other Protista in their 
cytology. We may group these cases in what the mathematicians 
would call an * interpolation formula/ which covers our present 
knowledge and which would run thus : Nuclear reduction is the 
reduction of the number of chromosomes due to the union of cells in 
fertilization to that found in a single gamete ; it occurs in the first 
protistoid divisions that occur after fertilization ; and is the necessary 
secondary result of fertilization , which would otherwise lead to the 
indefinite increase of the number of chromosomes by constant doubling. 
This view is due partially to Strasburger, partly to the writer. 
M. HARTOG. 
Queen’s College, Cork. 
