1 84 BOTANICAL GAZETTE. 



Eriodictyon glntiiiosum, Bentli.. as Illustrating' Evolution. 



(Plate II.) 



As a teacher I have often been ' perplexed to answer the ques- 

 tion of my pupils: why is it that to cells and tissues which so often 

 shade into each other and which usually present such small differ- 

 ences you give distinct names? To the more advanced investiga- 

 tor, however, the problem comes in another shape, i.e. how is it 

 that cells which start at first from a simple form of fundamental 

 tissue eventually become so unlike ? If the observer has allowed 

 himself to philosophize over this question he most probably has 

 learned to regard it as but another paragraph from the great chap- 

 ter on evolution, and can hardly have escaped a wonder that cell 

 variation is so little written or spoken of in this connection by 

 botanists. Cell growth and development, whether rightly or 

 wrongly, appear to have suffered a divorce from our ideas of specific 

 evolution, yet the latter could not exist without the former. Simple 

 parenchyma may be i?ll sufficient for every form of thallus ; but 

 before a true caulome can rear its head into the air, there must be 

 the differentiated, stiffening woody fibre; or before the hard-shelled 

 nut could be produced, sclerenchyma must have appeared. Evi- 

 dently then this differentiation has to do with success in the strug- 

 gle for existence. But with all this, in the great mass of plants 

 there appears to have come a settled average character in the dif- 

 ferent groups of cells and tissues; that is, differences marked 

 enough exist, but we can read them through from the outside to the 

 pith before ever a section has been made. On the other hand there 

 are others which we have come to recognize as likelj 7 to show devi- 

 ations from the regular order before we have examined them, though 

 we cannot tell what directions those deviations will take. Some of 

 these may serve to show evident connections between the different 

 cell types in places where we hardl}- expected to find such links. 

 I have recently been quite struck with this last class of facts in 

 studying Eriodkiijon glutinosum from the standpoint of practical 

 pharmacy, though the facts themselves were entirely outside the 

 objects I had in view, and have no bearing upon them. What I 

 desire to call attention to here are simply gleanings which lay oft, 

 but alongside, the pharmaceutical trail. 



A more striking instance of the connection between diverse 

 forms of tissue can hardly be imagined than that furnished by the 

 change from bast to sclerenchyma; the former being typically rep- 

 resented in the fibre which makes the napkins we use at the table, 

 and the latter in the shell of the hickory nut which defies our 

 youthful teeth. Yet figures 9 & 10 are taken from fibres in 

 the Peruvian Bark which are so nearly on the boundary line that by 

 some vegetable anatomists they are classed as bast and by others as 

 sclerenchyma. Isolated in the pulp of pears are found the gritty 

 grains of sclerenchyma, though from the same fundamental cells 



