262 Mr G. F. Scott Elliot on the 



The original cambium bundle is distinguished from the 

 peripheral embryonal layer, and the ground parenchyma by 

 its prosenchymatoid cells, with a narrow lumen. It is 

 formed among the primary meristem cells by longitudinal 

 division planes, and the horizontal cross walls of the pris- 

 matic cells thus formed become afterwards oblique. 



Growth. — Sachs holds that the direction of the new 

 division planes, in the case of a single initial cell, is wholly 

 determined by the form and growth of the embryonal tissue 

 considered as a whole. 



Haberlandt goes with much detail into this question, and 

 shows that the initial cell has probably an individual 

 determining influence on the formation of new division 

 planes, especially where these are transverse. 



I. Skin System. — One of the chief dangers of plant life lies 

 in excessive transpiration of water, which results in death 

 by desiccation, and it is the chief function of the skin 

 system to protect the plant against this transpiration. 



Probably it also protects the plant against the effects of 

 excessive illumination in the day time, and radiation of heat 

 by night. Also, in the case of winter buds, abrupt changes 

 of temperature are thus guarded against. It is possible to 

 verify the latter by direct experiment, as has been already 

 done, 



(a) Epidermis. — Treating the epidermis in this sense, it 

 will be seen that the epithelium of the roots and guard 

 cells of the stomata are not included in the skin system. 



In the outer wall of the epidermis there is, besides the 

 inner cellulose lamella, a cuticular layer, and there is also 

 the cuticle extending over the whole outer surface (this 

 cuticular layer and the cuticle containing a substance 

 cutin). Now, in water plants there is never any great 

 thickening of these last two layers (sometimes it is nearly 

 absent) ; while in all land plants it is present, and in plants 

 from dry climates (where the danger of desiccation is great), 

 it is often very pronounced. Hence probably this cutin is 

 the chief protection against desiccation. Many direct ex- 

 periments have been undertaken to show this ; for example, 

 apples from which the epidermis has been removed tran- 

 spire 55 times as much per hour per square cm., as those 

 in a normal state. The epidermis cells, seen from above, 



