STOKEY— ANATOMY OF ISOETES 3 2 5 



M with the characteristic areolations of their ^£**£Z~ 

 in various reactions with the sieve tubes of the leaf, with which we _A J - ^ 

 are continuous, are best to be regarded as themselves representing the sieve tubes 



of the stem. 



possibl 



oas given above might be aecepted as sufficient proof o. >"< > hl °™. 

 nature of the pitted cells, although the fact of a camb.um cutung ol 

 both phloem and xylem from the same face is so extraordmary.hu 



theory 



The 



elves with leaving the burden of proof to other investigators. i 

 onlv analogv is in the case of Dracaena and its allies, whose anonia tous 

 secondarv thickening has been frequently referred to in the Uterature 

 on Isoetes. Before Russow's theory made its appearance, the ^ue 



secondary xylem 



on me inside of tne camoium nau uccn x^ 5 «. .^ ^ 



Thi> was the very natural interpretation given by Hofmeist 

 Higher Cryptogamia and was accepted, apparently without qutfx , 



, a if nnp is not willing to 



until Russow's more critical work appeared. It one is n «~ ^ 



accept the Russow theory, the natural alternative is to r fe _ ^ 

 prismatic layer" as secondary xylem. This, of cour.e, «q ^ 



explanation of its unusual structure. 1 ne prc^u- ^ without 



of parenchyma in the secondary wood is unusual du ^ 



phloi os fuli^ 



ymoiosjuiiginosus. ine presence 01 ^-5- — r ^ int 



the situation which has led to controversy, and is hlocm _ 



to be explained. However, the presence of pitted cells F^ ^ 

 •ike aspect does not necessitate the gumption tha^ ^^ ^ 

 Phloem, since that structure is found in cells 01 ^.^ 



sample, the cortical parenchyma of Heiminuw,^ _ ^ ^ 



Farmer and Freeman (10) in their description ot tne p 



of the cortical parenchvma sav : . 



lv simple depressions 



The pits are remarkable, forming, as they do, not me « > of a s i e ve 



ln the walls, but rather being massed together in areas li ^ ^ diffcr 

 plate. Indeed thev mav fairlv be termed pitted areolae an 



essentially 



The presence of cells of this type in tissues ^ ^^ 



^long to part of the bundle indicates that pitted WW ■ ^ 



l nly to be taken as an indication of phloem. 



