18 GRACE E. COOLEY ON 



leaf. B, suction ol' the seed of the same plant, with testa removed ; ((, cotyledon ; 

 b, endosperm ; r, the same with reserve dissolved from the walls. The cotyledon acts 

 in four ways : to extricate the embryo from the seed; to protect the young bud ; to 

 break tlirough the soil; and to supply the young plant with nourishment. The source 

 of nourishment is the endosperm of the seed. An examination of a young seedling 

 is interesting. PI. 4, fig. 2, is instructive; it exhibits a section of the seedling, treated 

 with iodine. The endosperm has for the most part the characteristic red-brown color, 

 but near the cotyledon the cells are colorless, showing that reserve cellulose is no longer 

 present. The flat spoon-shaped tip of the cotyledon has enlarged somewhat and is tilled 

 with starch. The young stem and bud, as well as the sheathing part of the petiole, 

 contain starch. 



In lig. 3, a section of a seed from a, plant three inches higli is illustrated ; the 

 process of solution has gone still farther and nearly all the reserve material of the endo- 

 sperm is exhausted. Irregulai'ly arranged around the edge of the seed, cells can be 

 seen whose walls are still thickened with reserve. The solution has left the cells 

 intact, but they are easily separated from each other in the cutting of the sections. The 

 cotyledon does not grow as does that of the Polygonatum, crowding the exhausted cells 

 together in the endeavor to reach tlie material stored in the outermost layers. The 

 method is different. 



At a certain stage of development, when the vascular system is well formed, the 

 cotyledon in the seed ceases to grow, and the cells of the endosperm themselves act as 

 cjirriers of the material, which the cotyledon needs, from the distant cells, which are 

 still capable of furnishing it. 



These intermediate cells remain healthy; they are fdled with protoplasm, which 

 shows its activity by the rate and vigor of its streaming, and this goes on for some time, 

 even aftei' the cells are isolated from one another. They contain much oil in small 

 globules, and granular matters appear in the protoplasm. 



PI. 4, fig 4, shows an isolated cell from which the reserve cellulose is dissolved. Its 

 walls are clear and colorless with iodine. Streams of protoplasm run in every direction, 

 and much oily matter lies in the masses next the walls. At a a large oil drop is break- 

 ing up into tiny globules, which are swept in the current of protoplasm toward the 

 wall. The oil in these cells is colored only slightly by iodine, whereas osmic acid stains 

 it brown or Idack. Fehling's solution fails to detect more than the merest traces of 

 sugar. The cells are much freer of protein reserve matters than during the resting 

 winter stage, and large vacuoles are present. 



Their appearance in this particular is in strong contrast to those cells nearer the 

 edges of the seed, which are not yet affected by solution, as well as in contrast to their 

 own earlier state. 



