620 SECTIONAL TRANSACTIONS.— K. 



These large roots grow dcwn vertically from the rhizome and may be as much as 

 5 mm. in thickness and more than a metre long. 



The small roots are given out in all directions at right angles to the axis of the 

 rhizome. The large roots have an extensive lacunar cortex, and sometimes a hexarch 

 stele, and are exceedingly like the roots of some Calamites except that there is no 

 secondary thickening. There is, however, no sharp dimorphism, as roots intermediate 

 in size between the large roots and the small are found. Like all the other roots on 

 the adult plant of Equisetum, they arise in relation to a bud in the base of the leaf 

 sheath. Where the root connects on to the bud the vascular tissue is in the form 

 of a solenostele with a central core of sclerenchyma which is continuous with 

 sclerenchyma developed on the inner side of the vascular bundles of the stem at the 

 node. Large roots of a similar type have also been observed in Equisetum maximum, 

 E. sylvaticum and E. arvense. 



Prof. J. McLean Thompson. — On the Use of Vascular Anatomy in Problems 

 of Carpel Morphology. 



In recent years facts of vascular anatomy have been largely advanced in argument 

 on the history of the Angiospermic carpel. 



An attempt will be made to show that the carpellary vascular system is variable 

 even in a single species, and that it may be regarded rather as expressive of the 

 present state of the carpel than as evidence of past stages in organisation. The 

 points raised will be illustrated by reference to the development and adult structure 

 of the legume. 



Discussion on The Size Factor in Plant Morphology. (Prof. F. 0. Bower. 

 F.R.S. ; Dr. G. P. Bidder ; Prof. V. H. Blackman, F.R.S. ; Prof, 

 H. H. Dixon, F.R.S. ; Prof. J. H. Priestley ; Prof. A. C. Seward, 

 F.R.S. ; Dr. H. Hamshaw Thomas ; Prof. D'Arcy Thompson, 

 C.B., F.R.S.) 



Prof. F. 0. BowEE, F.R.S. — The principle of similarity has been applied freely in 

 the study of the animal body. Botanists have been slower in applying it to plants, 

 and then chiefly in the mechanical aspect. But the relationship of the principle to 

 physiological interchange commands a wider interest, since this is conducted through 

 limiting surfaces, external or internal. With increasing size, if the form be unchanged, 

 each limiting surface will increase only as the square, while the enclosed bulk will 

 increase as the cube of the linear dimensions. It may be assumed that, provided 

 the surface be uninterrupted and its character remains the same, such interchange 

 will be proportionate to the area of the surface involved. Accordingly in an enlarging 

 body, if the original form be maintained, a practical size-limit will constantly be 

 approached in respect of any tissue that is physiologically active, beyond which its 

 surface would be insufficient to meet the demand for transit. But any change from 

 a simple form which makes the surface more complex increases the proportion of 

 surface to bulk. Increasing complexity of form may thus be held prima facie as a 

 concession to physiological requirement in a growing organism. The size-factor which 

 favours such results is naturally only one among many that have influenced form. 

 Nevertheless a recogm'tion of the morphological results which do, in point of fact, 

 accord with the demands of increasing size, should help to make morphology a rational 

 study. 



In the primary construction of any ordinary vascular plant there are three limiting 

 surfaces of special physiological importance : (\)the outer contour, complicated though 

 its study is in sub-aerial plants by stomatal perforations and by cuticular develop- 

 ment ; (2) the endodermal sheath, which delimits the primary conducting tracts from 

 the enveloping tissues ; and (3) the collective surface by which the dead tracheal system, 

 faces upon the living cells that embed it. Each of these is a surface of physiological 

 transit, suitable for study from the point of view of the proportion of surface to bulk 

 as the size increases. 



The illustrations to be submitted wUl relate to (3), and chiefly to primary vascular 

 structure as seen in primitive plants. Here the common form of axis is conical, 

 enlarging upwards ; and the conducting system expands with the axis. The xylem- 

 tract at first consists of a sohd core, surrounded by living cells, The methods of 



