CHAP. II. BREAKING THROUGH THE GROUND. 81 



Megarrhiza Calif ornica. The cotyledons of this 

 Gourd never free themselves from the seed-coats and 

 are hypogean. Their petioles are completely con- 

 fluent, forming a tube which terminates downwards 

 in a little solid point, consisting of a minute radicle 

 and hypocotyl, with the likewise minute plumule 

 enclosed within the base of the tube. This structure 

 was well exhibited in an abnormal specimen, in which 

 one of the 'two cotyledons failed to produce a petiole, 

 whilst the other produced one consisting of an open 

 semicylinder ending in a sharp point, formed of the 

 parts just described. As soon as the confluent 

 petioles protrude from the seed they bend down, as 

 they are strongly geotropic, and penetrate the ground. 

 The seed itself retains its original position, either 

 on the surface or buried at some depth, as the case 

 may be. If, however, the point of the confluent 

 petioles meets with some obstacle in the soil, as 

 appears to have occurred with the seedlings described 

 and figured by Asa Gray,* the cotyledons are lifted 

 up above the ground. The petioles are clothed with 

 root-hairs like those on a true radicle, and they 

 likewise resemble radicles in becoming brown when 

 immersed in a solution of permanganate of potassium. 

 Our seeds were subjected to a high temperature, and 

 in the course of three or four days the petioles pene- 

 trated the soil perpendicularly to a depth of from 

 2 to 2J inches ; and not until then did the true 

 radicle begin to grow. In one specimen which was 

 closely observed, the petioles in 7 days after their 

 first protrusion attained a length of 2J inches, and the 

 radicle by this time had also become well developed. 

 The plumule, still enclosed within the tube, was now 



* American Journal of Science,' vol. xiv. 1877, p. 21 



