MORPHOLOGY 
aposporous gametophytes in ferns arise usually from checked sporangia, 
but sometimes directly from the leaf margin (usually a tooth), and occa- 
sionally from other regions of the leaf. 
An interesting question connected with apogamy and apospory is the effect on 
the number of chromosomes. A sporophyte has the double (diploid) number 
(2x) of chromosomes because it has come from a fertilized egg. Therefore, does 
an apogamous sporophyte have the reduced (haploid) number (*)? A gameto- 
phyte has the reduced number (#) because it has come from a spore produced 
by the reduction divisions. Therefore, does an aposporous gametophyte have the 
double number (a*)? Recent investigations, both among ferns and seed plants, 
indicate that both of these questions may be answered in the affirmative. 
Conclusions. The important features of this great group may be 
summarized as follows: There are represented all the pteridophyte 
types of vascular cylinder, from the most primitive to the most advanced; 
but the cylinders are peculiar among pteridophytes (Ophioglossales 
excepted) in being phyllosiphonic. The leaves are the most highly 
developed among pteridophytes (Ophioglossales excepted), being re- 
duced in number and increased in size. The sporangia are multiplied 
on the lower surface of the leaves; there is very little differentiation of 
foliage leaves and sporophylls; and there is no organization of strobili. 
The conspicuous features are the development of the leptosporangiate 
habit, found in no other group of vascular plants (water ferns excepted) ; 
and along with this the appearance of a special kind of antheridium devel- 
opment. There is a gradual diminution of spore output per sporangium, 
and a corresponding diminution of sperm output; also a persistent re- 
tention of homospory. The gametophyte is a thallose, aerial structure. 
The line as a whole appears to be highly specialized, the only group con- 
taining the possibilities of the higher plants being the Marattiaceae, 
probably the oldest family. 
(b) Hydropteridineac 
General character. The water ferns are probably an aquatic 
branch from the true ferns that has developed heterospory. They 
are leptosporangiates, and hence are doubtless derived from the only 
other known group of leptosporangiates. They comprise two distinct 
families that seem to be of separate origin. It is evident, therefore, 
that heterospory has arisen independently in almost every group of 
pteridophytes. 
