184 SECTIONAL ADDRESSES. 
a minor detail, so long as it produces asexual tetrads.’ He himself deals 
with all these somatic considerations with great thoroughness, as may 
be seen from the following selection from the numerous sectional headings 
of the memoir: ‘ Evolution of growing-points’; ‘Systems of Ramifica- 
tion’; ‘Symmetry’; ‘ Phyllotaxis’; ‘Space form and the Theory of 
Members’; ‘ Evolution of the Leaf-member’; ‘ Pneumatocysts and 
Pneumatophores’; ‘Evolution of Gametophores’; ‘Theory of Tissue 
Differentiation’; ‘Mechanism of Tissue Differentiation’; ‘ Mucilage- 
hairs and Ducts,’ &c. All these are treated philosophically, and the 
relation of various structures to the factors of the environment expounded 
with a thorough mastery of detail. 
In the course of the work a classification is given of Plant-forms, 
arranged in order of increasing complexity and efficiency. Though in 
matters of detail the author could improve the classification in respect 
of clearness and consistency, it is sufficiently interesting to justify our 
indicating, in mere outline, the principal forms dealt with. 
The series begins with: 1. Ectocarpoid Forms, consisting in Hctocarpus 
and Pylaiella of much branched, uniseriate filaments. The outstanding 
advantage of this form is that every cell unit is fully exposed to the 
external medium ; the inevitable disadvantage of the form is its weakness 
to withstand heavy seas : this also prevents its attaining a great size. 
Sphacelaria is so different from the above that one would have pre- 
ferred its being placed under a different heading. It is remarkable for 
its big apical cell, and the multiseptation of its products, with very little 
or no intercalary growth. This gives greatly increased strength, but the 
plants remain small. In the higher members the central cells in the 
older axes receive less light, and are not in contact with the external 
mediums. 
Cladostephus, by further outgrowths from the primary cortex, develops 
a ‘mantle’ or secondary cortex which greatly increases its mechanical 
strength. One would have preferred to include this under the ‘ Cortzcated 
Forms’ rather than among the ‘ Ectocarpoid Types.’ 
2. The Cable Type with axial strands of large cells or filaments, often 
strengthened by interwoven hyphal outgrowths ; the whole invested with 
tufts of branches radially arranged in a palisade-like manner and embedded 
in a matrix of mucilage. These ‘ ultimate ramuli’ carry on the work of 
photosynthesis and also bear the reproductive organs. Mesogioia is an 
example of this type, while Chordaria shows considerable advance in 
condensation and efficiency. 
3. The Multiseptate Cable Type—Apart from a few small plants, 
Chorda is the only example given of the type. It interests the author 
greatly as he sees in it a transition from the ‘ Cable Type’ to the ‘ Paren- 
chymatous Type.’ The only reason for connecting Chorda with Mesogloia 
or Chordaria is the fact that the whole surface, except the basal part, is 
covered with paraphyses and sporangia. It may, however, be pointed out 
that in its parenchymatous structure, its possession of well-developed 
trumpet-hyphe, in the structure of its reproductive cells, and in the nature 
of its alternation of generation, Chorda is a true Laminarian ; and, as will 
be shown later, it isfar nearer Laminaria itself than Saccorhizais. For this 
reason it is difficult to see why a separate division should be made to receive 
this plant-form. The author’s remarks about the efficiency of the form are 
Aw T=. | 
