1896. NOTES AND COMMENTS. i49 



indistinguishable from the other cortical layers. On this assumption 

 the great stumbling-block, Equisetum, is easily removed. Formerly we 

 were bothered by the vagaries of the endodermis, which sometimes 

 surrounded each bundle, sometimes formed a double ring bounding 

 the bundle-system towards both the cortex and the pith, or sometimes 

 behaved properly and ran round the outside only. Now, if we 

 imagine instead a phloeoterma, which in every case surrounds the whole 

 bundle-system, having, in the two last-mentioned cases, the characters 

 of an endodermis, and, in the first, no character at all by which we 

 can distinguish it, we bring Equisetum into a place in the theory as a 

 monostelic plant. 



In stems of ferns and selaginellas, in the roots of a few palms, 

 and in the stems of Gunnera and species of Auricula, among dicotyle- 

 dons, something different occurs. The single stele of the root, in 

 passing through the hypocotyl, breaks up into several steles. In such 

 cases the stem or root is polystelic, each stele containing bundles of 

 wood and bast, separated by conjunctive tissue, surrounded by a 

 pericycle, and bounded at the cortex by the phloeoterma, which 

 generally shows endodermoid characters. As the student who has 

 cut sections of the bracken-fern will remember, the steles are not 

 always cylindrical, but may be oval or drawn out into a band ; in fact, 

 they may show considerable variation in shape. 



Finally, the term schizosteh, or mcvistde, is applied to those 

 portions of the stele, or steles, of the stem which run up into the 

 petiole and, as in Pinus, continue unbroken through the leaf, or, as is 

 generally the case, branch repeatedly in the flat, expanded blade. 

 The advantage of the stelar theory is that it supplies what we have 

 hitherto wanted, a general standpoint from which to view the internal 

 anatomy of the plant axis and its branches. It directs attention to 

 the vascular system as a whole, and not, as hitherto, to the vascular 

 bundle, which, implying very different things in different cases, does 

 not admit of a comparative treatment. 



Plant Evolution. 



There are often several ways of looking at the same thing. A 

 flower, for instance. We were wont to define it as a shoot modified for 

 purposes of reproduction. Goethe's Ur-plant showed how the petals, 

 sepals, stamens, and carpels were after all only leaves which, in virtue 

 of their respective functions in connection with the ultimate object of 

 forming fruit containing seeds, assumed shapes difl"ering more or less 

 widely from what we generally associated with the term leaf. That 

 is to say, the popular leaf being the flat expanded green fohage-leaf, 

 we felt constrained to derive the floral leaves from such a one. We 

 could fold one up nicely to make a carpel, but stamens floored us 

 rather, and we rejoiced over the water-lily, which showed us how it 

 had all happened, supplying a complete transition from the flat 



