12 



gave exactly the same results. The pith in the upper internode 

 within each cast was living, while it was dead but not collapsed in 

 the lower internodes within the casts. Above and below each cast 

 was a large central cavity. Except the addition of a few vessels in 

 each bundle and the obliteration of intercellular spaces there had 

 been no changes within the casts. Above and below the cast in each 

 plant cortical cavities had appeared, the cambium-zone had been com- 

 pleted, and the cambium and the outer pith-cells had given rise to 

 a few thick- walled elements. Within the casts no cells were thick- 

 walled except the collenchyma at the angles of the stem, and this 

 condition of this tissue was present before the casts were applied. 

 The bundles had not grown so much within as without the casts; 

 within, vessels were smaller and somewhat crumpled. 



In both plants the mechanical tissue was better developed at the 

 upper limit of the casts than within or farther above. 



Ciicurbita pej)o L. 



In the aerial parts of Cucurbita pepo the cavity is present every- 

 where before elongation has ended, and everywhere, except in the 

 hypocotyl and the flower stalk, before enough surface of an internode 

 has been exposed for the application of a cast. When however a cast 

 is applied to a young hypocotyl not later than the unfolding of the 

 cotyledons, or is applied to the flower-stalk, there is a cessation of 

 growth lasting for a week or more. In 3 flower-stalks put into casts 

 2 of them soon died and the 3d in a period of 2 weeks developed 

 no farther except to increase in thickness by the expansion of cells 

 above and below the cast. Out of the large number of very young 

 plants whose hypocotyls were put into casts, 10 grew but only a few 

 grew well. The plant sometimes forms a thick swelling just above 

 the cast and sometimes has only the normal thickness. If the cast 

 is applied after the plant has produced several leaves, the disturbance 

 of growth is much less. 



The cavity appears first as a schizogenous split in the middle of 

 the pith, the separation of cells being soon followed by their 

 death. As the cavity enlarges the tangential pull on the cells 

 bounding the cavity is plainly indicated by the distortion there 

 evident. The cambium-zone is not completed for some time after the 

 cavity appears. 



1. Examination after 28 days. About the hypocotyl of this plant 

 the cast was applied when the first leaf between the cotyledons was 



