Zea mais L. 



From a young plant of Zea mais that had several lower inter- 

 nodes fully extended the leaves were cut away so as to expose several 

 of the upper internodes when each was not more than a centimeter 

 in length. About these internodes a gypsum cast was placed, and 

 the plant allowed to grow farther. At the end of 37 days the plant 

 was cut for examination. Several internodes had elongated above the 

 cast and a good growth had been made. The diameter of the stem 

 above the cast was no greater than that within. 



The microscopic examination of the internodes that the gypsum 

 had not allowed to elongate showed there much weaker bundle-sheaths 

 than above and below; the usual thick-walled and lignified peripheral 

 zone of fundamental tissue was absent, though present in the normal 

 parts of the same stalk. Within the cast the air-canal in the bundles 

 had not been formed; the surrounding thin-walled cells could be seen 

 in cross-section to connect directly with the vessel which is normally 

 destroyed in the formation of the air-canal. 



Four other plants of this species when the internodes were all 

 very short and not more than 3 cm or 4 cm above the earth were sur- 

 rounded by gypsum at the level of the earth without removing the 

 leaves. The plants thus grew in length within the casts but not 

 much in thickness. One plant was examined after a lapse of 23 days, 

 the other 3 after 60 days. All grew as well as normal ones in the 

 same pots, the older plants reaching the blossoming stage and being 

 a meter in height. The enlargement of the stem above the casts 

 was not sudden but very gradual, extending over one or more inter- 

 nodes. The thickness of the stems within the casts was probably two 

 thirds of what they would have been normally. 



Three of these plants showed the normal amount of mechanical 

 tissue present within the casts. Cells of all kinds and vessels were 

 of smaller cross-section within than above and below the casts. The 

 fourth plant was one of those that grew for 60 days after casting. 

 The difference in diameter between the part in the cast and that 

 without was greater here than in any of the other three. In its 

 histological structure it showed less mechanical tissue in the con- 

 stricted part than above and below, though the difference was not 

 so great as present in the first plant described where the internodes 

 had not elongated. 



