100 R. J. ANDERSON [august 



plant to consist of columns of dodecahedral cells, arranged so that 

 the upper surface of one cell might coincide with the base of the one 

 next above it. If the adjacent columns fit as nearly as possible into 

 one another, that is to say, that the re-entrant angles of one column 

 may correspond to the salient angles of the other, three dodecahedra 

 will meet at each edge, but, since the angle of a dodecahedron is less 

 than 120°, they will not fill the space, but will leave interstices, increas- 

 ing in width from the centre of the mass towards its circumference. 

 The " tubes " will find room to grow in these interstices, and the growth 

 will be effected by the addition of matter externally as in exogens. 

 The increase is likely to be more considerable where the edges meet, 

 that is, at the angles of the pentagon, than elsewhere. Certain quali- 

 fications are, however, introduced. If the cells are icosahedral and 

 arranged in the same manner, it is easy to see that, their angles being 

 greater than 120°, the interstices would be formed internally, and that 

 the growth of such a plant w r ould proceed by the internal addition of 

 matter as in so-called endogens. In this case, as in the exogens, the 

 growth should take place along planes passing through the angular 

 points. Hence the parts ought to be arranged in threes in the one 

 case and in fives in the first. The parts in the fructifying organs of 

 certain fungi and mosses are in number powers of two, so, it is pointed 

 out, that the cubical arrangement in acotyledons is rendered probable. 1 

 This ingenious hypothesis (" Une idee au moins piquante et ingenieuse," 

 says De Candolle) was propounded in the earlier years of the present 

 century. The elements, although angular, unite to form tissues with 

 round outlines. The form assumed is the result of various forces. 

 Equally diffused pressure acting along the radii of a cylinder tends 

 to maintain its form. A cone would have its shape best maintained 

 by the diffusion of the pressure according to a certain law ; but here 

 again the internal activities, surface tension of cells, perhaps, and other 

 agents, may materially modify the results. 



One cannot venture to compare the increase in size of a crystal to 

 the deposit of a soluble salt from an evaporating solution, but rather 

 to the growth of a battalion of soldiers by more men falling into rank 

 all round at the word of command. Even in crystals many are the 

 causes that affect the increase in size and form ; temperature and 

 impurities in the substance are two of the best known. The " growth " 

 here is, of course, influenced by the supply of material. Organic 

 bodies, also, are influenced by many activities that start from without 

 and reach into their substance. Their growth is true growth, but 

 within considerable limits the physical demeanour of the organic may 

 correspond to the inorganic. 



One might compare a slender shoot to a six-rayed ice crystal that 

 is growing slowly by the addition of an upward stream of water. 



1 Abbreviated from Allman's paper. The term "tubes" appears to have been used to 

 indicate vessels and fibres of plants as distinguished from cells proper. 



