20 METASPERMAE OF THE MINNESOTA VALLEY. 
based upon the presence or absence of sexuality. We have, 
therefore, the two great divisions: 
A. PRoTOPHYTA: Plants in which sexuality has not been 
developed and in the ancestral line of wiich itis believed, from 
collateral evidence, that there are no sexually complete 
progenitors. 
B. MetapHyta: Plants which manifest sexuality or indicate 
by accessory characters that in their ancestral lines there have 
occurred sexually complete progenitors. 
These two great divisions are not clearly delimited, owing to 
the presence of transition-forms which unite the lower group 
with the higher. Suchaform is the well known Ulothrix zonata 
in which certain cells function indifferently as spores or 
gametes (marrying cells). Furthermore, the limits are ob- 
scured by such reduced forms of the Metaphyta, as undergoing 
retrograde metamorphosis, have lost their sexual characters 
and often resemble closely the upward-tending types of the 
Protophyta, which are acquiring sexual characters, or on the 
point of acquiring them, one might say. Such intermediate 
forms, whether rudimentary or reduced, render exact limita 
tion of the two great divisions quite impracticable. 
In similar fashion it is possible to arrange the Metaphyta in 
two subdivisions based upon the development of the fertilised 
egg. In the lower forms, after fertilisation, the egg proceeds 
to develop a plant like the parent, which produced the egg; in 
the higher forms, the egg undergoes a preliminary subdivision, 
the result of which is the ultimate development of few or very 
many cells, each of which is normally capable of producing a 
plant like one of the parents. We therefore have the two fol 
lowing subdivisions: 
I. GaMmopHyta: Metaphyta which normally develop sexual 
plants from their fertilised eggs without the interpolation of 
any spore-producing structure. 
II. SporopHyta: Metaphyta which normally subdivide 
the fertilised egg into a cellular structure, capable of growth, 
all or part of which consists, when mature, of spores, from 
which sexual plants are normally produced. Such a cellular 
structure is called a sporophyte or sporophytic plant. 
Examples of I. are the lower Zygophyta and Ovphyta of Bessey 
(82), plants like the pond-scum (Zygnema) or the black-mould 
(Rhizopus, Mucor): examples of II. are too numerous to men- 
tion, for in this subdivision are all plants inclusive of, and higher 
(82) Bessey: Text Book of Botany, 6 ed. (1889). 
