103. Parenchyma of maize, shewing the same phenomenon . . . 298 104, 5. Diagrams of the partition-wall between two soap-bubbles . . . 299, 300 106. Diagram of a partition in a conical cell . . . 300 107. Chains of cells in _Nostoc_, _Anabaena_ and other low algae . . . 300 108. Diagram of a symmetrically divided soap-bubble . . . 301 109. Arrangement of partitions in dividing spores of _Pellia_ (Campbell) . . . 302 110. Cells of _Dictyota_ (Reinke) . . . 303 111, 2. Terminal and other cells of _Chara_, and young antheridium of _do._ . . . 303 113. Diagram of cell-walls and partitions under various conditions of tension . . . 304 114, 5. The partition-surfaces of three interconnected bubbles . . . 307, 8 116. Diagram of four interconnected cells or bubbles . . . 309 117. Various configurations of four cells in a frog’s egg (Rauber) . . . 311 118. Another diagram of two conjoined soap-bubbles . . . 313 119. A froth of bubbles, shewing its outer or “epidermal” layer . . . 314 120. A tetrahedron, or tetrahedral system, shewing its centre of symmetry . . . 317 121. A group of hexagonal cells (Bonanni) . . . 319 122, 3. Artificial cellular tissues (Leduc) . . . 320 124. Epidermis of _Girardia_ (Goebel) . . . 321 125. Soap-froth, and the same under compression (Rhumbler) . . . 322 126. Epidermal cells of _Elodea canadensis_ (Berthold) . . . 322 127. _Lithostrotion Martini_ (Nicholson) . . . 325 128. _Cyathophyllum hexagonum_ (Nicholson, after Zittel) . . . 325 129. _Arachnophyllum pentagonum_ (Nicholson) . . . 326 130. _Heliolites_ (Woods) . . . 326 131. Confluent septa in _Thamnastraea_ and _Comoseris_ (Nicholson, after Zittel) . . . 327 132. Geometrical construction of a bee’s cell . . . 330 133. Stellate cells in the pith of a rush; diagrammatic . . . 335 134. Diagram of soap-films formed in a cubical wire skeleton (Plateau) . . . 337 135. Polar furrows in systems of four soap-bubbles (Robert) . . . 341 136–8. Diagrams illustrating the division of a cube by partitions of minimal area . . . 347–50 139. Cells from hairs of _Sphacelaria_ (Berthold) . . . 351 140. The bisection of an isosceles triangle by minimal partitions . . . 353 141. The similar partitioning of spheroidal and conical cells . . . 353 142. S-shaped partitions from cells of algae and mosses (Reinke and others) . . . 355 143. Diagrammatic explanation of the S-shaped partitions . . . 356 144. Development of _Erythrotrichia_ (Berthold) . . . 359 145. Periclinal, anticlinal and radial partitioning of a quadrant . . . 359 146. Construction for the minimal partitioning of a quadrant . . . 361 147. Another diagram of anticlinal and periclinal partitions . . . 362 148. Mode of segmentation of an artificially flattened frog’s egg (Roux) . . . 363 149. The bisection, by minimal partitions, of a prism of small angle . . . 364