148 SCIENCE PROGRESS. 



layer of the cortex does not always possess the special 

 thickenings which give it the right to be called a 

 " membrane," Strasburger objects to Van Tieghem's re- 

 definition of the word endodermis, and proposes to sub- 

 stitute the term Phloeoterma, to be applied to the inner 

 layer of the cortex, i.e., to be used in the strictly morpho- 

 logical sense, whether this inner layer has special characters 

 or not, and to reserve the term endodermis in accordance 

 with its original sense for any sheath or membrane com- 

 posed of cells with suberised radial walls or other dis- 

 tinctive thickenings, without reference to its position. 

 This revised terminology certainly helps us to get rid 

 of the confusion of thought manifested in Van Tieg- 

 hem's use of the word endodermis. Strasburger concludes 

 that as all species of Equisetum agree in possessing a ring 

 of simple collateral bundles, they should all be considered 

 monostelic, whether the phloeoterma be developed as a 

 general endodermis, or each bundle possess a special 

 endodermis, the phloeoterma having no characters by which 

 it can be distinguished. The same considerations would 

 apply to the genus Ranunculus and the other cases of 

 "astely ". While we must fully admit the general force of 

 his argument on the ground of comparative anatomy, it is 

 difficult to agree with the following sentence : " Die 

 Grenze der Rinde gegen den Centralcylinder ist dort wo 

 sie sich nicht besonders als Endodermis oder Starkescheide 

 markirt, nur theoretisch zu ziehen, dieselbe ist aber flir alle 

 Falle festzuhalten ' : (15, p. 484). How is one to "hold 

 fast " a limit which one cannot distinguish ? We can only 

 refer to the remarks which have been already made upon 

 this subject, but we shall briefly recur to the subject in 

 considering the development of the stele. 



Leaves furnish us with excellent examples of the frequent 

 impossibility of separating stelar from extra-stelar tissue. 

 Putting aside those cases in which one or more steles 

 from the polystelic stem directly enter the petiole 

 [Gunncra, Ferns), we have to consider the ordinary 

 case in a flowering plant, where we have one or more 

 bundles leaving the cylinder and passing into the petiole. 



