322 BOTANICAL GAZETTE [aprii. 



that the " prismatic layer" is composed of several kinds of cells. In 

 the four species studied there is a considerable range both in the typi 

 of cells and in their distribution. 



■P 



rather large number of active nucleate parenchyma cells, whose wall 

 are slightly thickened. Associated with them are other cells which 

 are almost or entirely empty and whose walls are not uniformly 

 thickened, but have round, oval, or irregular pits. In such cells the 

 thickening is not very heavy. There are usually other cells in which 

 the thickening is more pronounced and is arranged in irregular banch 

 or rings. In some cells there are heavy bands in addition to th 



irregular pittings. 



Of the four species, /. Tuckermani var. Harveyi most closely 

 resembles the preceding species, but it differs in several points. There 



parenchyn 



elh 



whose walls are thickened irregularly. These cells are seldom entirely 

 empty, but usually contain a little protoplasm and small, apparent j 

 degenerating, nuclei. The cells are for the most part of the type 

 shown in fig. 23, in which the pits are small and irregularly dhtn >- 

 uted, and there are but faint indications of banding. In the older 

 plants, however, it is not uncommon to find the thickening fornnn 

 more or less definite bands. In the older parts of old plants the J» 

 become smaller and less prominent, tending to disappear en X- 

 Sometimes the pits can be seen in sections stained in Bismarck >rown, 

 when with a less transparent stain, such as Delafield's ^ mat0X -J; 

 the pits cannot be distinguished, and the walls appear to hav ^^ 

 form and rather heavy thickening. Apparently the thicken "! g kening 

 cell wallsgoes on through a period of several years, the first ^ tf 

 being irregularly distributed, leaving irregular pits, while I e 

 deposits include the whole of the wall and tend to obliterate t J P^ 

 In /. melanopoda we have all the types of cells which cell>; , 

 described for /. echinospora var. Flettii: active parenchyma ^ 

 pitted cells, and cells with irregular thickened bands or ring * ddJtion 

 pitted and banded cells are as a rule entirely empty- "^^ 

 to these types of cells, however, there are other cells wltl h ' ira i 

 thickenings which are slightly lignified, and also tracheids *i 



of the 



or annular thickenings, whose lignification is pronounced, a 



