174 
Trow. — Observations on the Biology and 
be referred to atavism. Why not refer them to the same 
category as other variations? The attempt might then be 
made, if not to refer them to their causes, at least to study 
them on the same lines as other variable characters. Let 
us at any rate keep our minds open to the probability that 
those external conditions which induce apogamy may be just 
those which bring about alterations in the structure of the 
nucleus. It is at any rate significant that in the typically 
apogamous oogonia of Saprolegnia Thureti we have an 
apparently unnecessary division in the gametangia, and a 
gameto-nucleus develops into a zygote-nucleus without fusion 
with another gameto-nucleus. There is too at least a pro- 
bability that apogamy in the Ferns is brought about by 
alterations in a group of cells effected under the influence 
of certain external conditions. The changes in the nuclei 
are more likely to be brought about by growth in this case 
than by fusions. 
Let us endeavour to keep in mind the probability that the 
same morphological elements may, in different plants, be cor- 
related with diverse physiological functions, and in the same 
plant, and at the same time, have more than one type of work 
to do, and we shall be a little nearer to the elucidation of the 
meaning of reduced nuclei. 
It is foreign to the purpose of this investigation to pursue 
these theoretical considerations further, but it may help to 
turn inquiry into a profitable channel if a sketch be appended 
to show the possible order of development of plant-forms 
according to this view. 
Asexual forms without sporangia 
I 
Asexual forms with sporangia 
Sexual forms. Reducing-divisions take 
place in the gametangia. No true 
alternation of generations : 
e.g. jFucus, Dictyota, Achlya and 
Saprolegnia : 
possibly Rhopalodia , Navicula and 
Brebissonia. 
Sexual forms. Reducing-divisions take 
place in sporogenesis. 
A true alternation of generations : 
e. g. Muscineae, Vascular Cryptogams 
and Spermaphytes : 
Cystopus (?) according to Berlese (’97) : 
possibly Spirogyra , Closterium and 
Cosmarium . 
