Cutleria multi fida ( Grev . ). 105 
Again, in the Cutleriaceae, the presence of the filamentous 
stage is clearly marked 
(1) The mature plant itself is but a fasciated structure of 
which the growing regions are still in the purely filamentous 
form ; the assumption of growth by intercalary division, as 
opposed to the primary apical growth, being general through- 
out the whole group of the Phaeosporeae. The reproductive 
portions of the thallus are still wholly in the filamentous 
condition,, and filaments bearing reproductive organs can be 
induced to grow and attach by rhizoids ; while the attach- 
ment-disc is also a mere felted mass of rhizoids ; the only 
portion of the thallus, in fact, which is not filamentous being 
the highly specialized assimilative region. 
(2) The filamentous condition is characteristic of the em- 
bryogeny for a short period in the foot-embryo, but persisting 
to the adult condition in the protonematoid embryos which 
produced antheridia in the Plymouth cultures, as also in the 
female form C. confervoides found at Heligoland by Kuckuck. 
In the evolution of the vegetative thallus from such a simple 
filamentous form, in which intercalary growth of the branches 
supersedes the original apical development, the first step in 
advance is marked by the regular segmentation of the cells of 
the main axes, by successive divisions by walls in planes at 
right angles to one another, leading to the more or less regular 
formation of a multicellular condition such as exists iq. many 
Phaeosporeae, e. g. simpler Sphacelarias, Myriotrichia , Des- 
motrichum. This massive type of thallus with purely radial 
symmetry is represented (1) by the foot-embryo, (2) by the 
basal region of the plant in the protonematoid embryo. In 
the same way this method of segmentation is ontogenetically 
repeated in the formation of sterile hair-like branches on the 
adult thallus. 
As an example of such a plant-form in which the cortical 
cells send out basal lobes forming a dorsiventral disc around 
the point of attachment of the plant, Sphacelaria cirrhosa may 
be instanced ; and it is clear that in the Sphacelariaceae 
differentiation has proceeded in two lines from such a simple 
