22 



In the upper part of the portion within the cast in the plant of 

 greatest growth there was a minute spot in the middle of the cross- 

 section filled with a few fragments of cell -walls. The conditions 

 existing within the abnormal parts in the 2 preceding cases existed 

 here also. The only difference noted was that there had been in 

 this 3rd plant more elements formed within the bundles than in the 

 other two. But all of these elements here as in the other cases had 

 remained thin-walled. In a normal plant of a development such as 

 this one had at the time of application of the cast and sectioned 

 in like position, the number of thick- walled vessels in an average 

 bundle was 8 to 10; the number of vessels whose walls had not 

 become thick 15 to 18. Within the cast the vessels of like descrip- 

 tion numbered thick -walled 12, thin -walled 28 to 30. Above the 

 cast in the same plant there were in an average bundle 40 thick- 

 walled vessels and 12 thin-walled. Though the number of vessels 

 thus seem in the abnormal part to be about 4 / 5 tnat in the normal 

 part of the same stem above the cast, the diameters of the stem at 

 the 2 positions are as 5 to 9. The cross-section of an average bundle 

 within the cast is also, proportionally to that of such a bundle above 

 the cast, very much less than the number of vessels would seem to 

 indicate; for within the cast all bundle -elements are much smaller 

 than their normal size, and all bundles lack a wide band of mechan- 

 ical xylem which is present in the normal parts of the stem just 

 centrally from the cambium. 



Thus there are presented in this stem, in 2 positions within 15 ram 

 of one another, one section with mechanical tissue represented only 

 by the very weak collenchyma in the cortex, and the other section 

 in which the collenchyma is very strong, ' the hard bast well developed, 

 the xylem well provided with mechanical elements and a bridge 6 

 or 7 cells deep, with strong walls, extending through the outer part 

 of the pith from bundle to bundle. 



In the lower part of this 3rd cast, the portion of the stem there 

 enclosed belonged to an internode below that last described, and 

 hence was much thicker. The cavity there present when the gypsum 

 was laid around it had since been filled by the inward growth of 

 all tissues, all showing cells much radially elongated, and a little 

 mechanical tissue had appeared in the cortex, in the phloem and on 

 the inner border of the xylem bundles. The mechanical tissue a 

 little below this position and hence outside the cast was almost in- 

 comparably stronger. 



In all these plants the stem at the upper limit of the cast showed 

 more thick-walled tissue than normal especially in the outer part of 



