IN PTERIDOPHYTES 201 
The genus Se/agzned/a includes eight species which are isophyllous, and 
over three hundred which are anisophyllous in the vegetative region. An 
intermediate condition is found in .S. sanguénolenta, which has accordingly 
been investigated by Goebel.! He found the dorsiventral structure to 
arise under the influence of external factors, such as moisture and shade. 
In certain strong-growing species, such as .S. cazlescens, the upright axes 
may be isophyllous, and the dorsiventrality only become pronounced in 
op 
A small plant of Danaea alata. st=stipules. (After Campbell.) 
the plagiotropic upper branches. Others may be dorsiventral from the 
first. Thus the genus illustrates gradual steps of dorsiventral development, 
such as have been noted in Lycopodium and Vaccinium, though the details 
are different. And the same conclusion may be drawn as in those cases, 
viz. that the radial is the primitive form, and the dorsiventral the derivative. 
The Fern-shoot, notwithstanding the preponderance of its leaf-develop- 
ment, may be examined from the same point of view as other Pteridophytes. 
The ancient Marattiaceae illustrate a probable initiation of dorsiventrality 
of the shoot within their own phylum. The young sporophyte seedling 
1 Lic. ps 105. 
