, 02 GROWTH AND ORIGIN OF MUTTICELLULAR PLANTS. 
the pioneers of plant-life, spherical cells predominate, due to the 
equal ic ) 
ants. we pass upwards in the developmental scale of algal 
life, it will be shown that other factors also play a part in deter- 
ining the mode of cell-growth and branching, due to increased 
potentiality of protoplasm in effecting differentiation and rearrange- 
mane of its own substance 
. 
unicellular Algee the tendency to form colonies is due to the 
bution from their primordial aquatic home, and encroach by degrees 
on land surfaces, as illustrated by Nostoc. In the British Palmel- 
lacee, six of the rarer Species, included under four genera, are 
solitary, or in very small groups, and remain aquatic; whereas four 
genera, forming gelatinous colonies, include twenty-one species, 
most of which are widely distributed on damp surfaces. This 
primitive method of guarding against desiccation, when plants are 
exposed to dry air, was early superseded by differentiation and 
cuticularisation of the external sheath; nevertheless it is interesting 
e considered as forming 
Was fo: 
the plant itself.” 
= especting the origin of the secretion, the author says :— 
T saw plainly that the mucus, which was poured out in such 
was wri 
later researches of Klebs, as mentioned above, also by Gardiner 
and Ito.+ 
Plants remain unicellular so long as the tendency of the proto- 
plasm to resolve itself into a sphere, after cell-division, predominates 
‘ Nan oe 4 new genus of Hepatice,’ Journ. Bot. 1876. 
: Structure of the Muc ilage-cells of Blechnum occidentale L. and 
Osmunda regalis L.’ Read betore the Royal Society, June 16th, 1887. 
