27 



collapsed elements. More mechanical tissue had developed in both 

 phloem and xylem, and the cells of the fundamental tissue bounding 

 the bundle-ring toward the centre had become thick-walled. Above 

 the cast was a good-sized cavity in the pith, and below the cast was 

 one the diameter of a single cell. 



Within the cast, in the cross- section studied, in two places just 

 beneath the first hypodermal row of cells there had been for the 

 length of several cells a slight crushing of tissue, the space thus 

 afforded having been completely closed up again. In cambium-for- 

 mation there has been a little progress from the last plant described, 

 since the primary cells between the bundles have become elongated 

 and in most place chambered, though nowhere has secondary tissue 

 arisen between the bundles. In the phloem the cells which normally 

 become thick-walled have increased in size in cross-section, but they 

 have not attained the size of the normal thick-walled cells and none 

 of them have become thick-walled. In the xylem the number of 

 vessels has slightly increased in each bundle. All of the primary 

 vessels and all of the earlier secondary vessels have been completely 

 flattened together, while the vessels more recently formed are of the 

 usual shape, but of smaller size. Among these recently formed vessels 

 are a few thick-walled xylem parenchyma cells. In the pith there 

 is no cavity and the cells are living. At the sides of each bundle a 

 few cells of the fundamental tissue have become thick-walled and 

 lignified. In these 2 places where mechanical tissue has made its 

 appearance. — in the xylem and flanking the xylem bundles, the 

 mass is extremely small when compared with the amount in similar 

 positions in the normal structure. 



In this preparation, as in the preceding, the great increase in 

 mechanical cells at the upper limit of the cast is noted. 



4. 55 days after application of cast. Two plants of equal age 

 and like treatment were examined. Both of them were well supplied 

 with blossoms and had reached a height of about a meter, though 

 one of them was not so strong a plant as the other. In both, the 

 tissues above and below the casts were well developed, and well 

 supplied with thick-walled, supporting cells. The weaker plant had 

 no cavity below the cast — this was normal since it was in the 1st 

 epicotyledonary internode — but had a large cavity above the cast; 

 the stronger plant had a cavity below the cast — in the 2nd epico- 

 tyledonary internode — and also one above. There were no cortical 

 cavities, but the tissue was very loose. 



The weaker plant showed within the cast the same condition of 

 tissues as noted in the plant 43 days in gypsum, except that within 



