PI XL T S SYL VESTRIS. l6l 



t/. Near the outer end " of the embryo-sac, one or two 

 much larger cells, the archegonia or corpuscula." 

 Observe the distinct row of endosperm cells, 

 smaller than the others, which surrounds the arche- 

 gonia. 



r. Occasionally one or two pollen grains having 

 shed the extine, may be found in the micropyle, 

 and still more rarely, some may be found which 

 have begun to emit their tubes. 



s. Make a diagram of the ovule and all its parts, 

 together with the wing and carpellary scale. 



ANNOTATIONS. 



The Scotch pine raises a strong tall stem above the 

 ground for the purpose of better exposing its leaves 

 and fruits to the air and sunlight. This habit is cor- 

 related with the excessive development of the fibro- 

 vascular system, which includes all the tissues of the 

 mature stem, with the exception of a trifling amount 

 at its center and circumference. 



Not only is there provision for continued growth in 

 length by the formation of terminal buds, as in Adi- 

 antum, but there is also provision for growth in diameter. 

 A part of the tissue, from which the fibro-vascular 

 bundles are formed, lying between the xylem and 

 phloem, retains the power of division and by annual 

 increase in the number of cells, chiefly in a radial 

 direction, the thickness of the bundle is increased. The 

 difference in the size and shape of the cells added to 

 the xylem in the spring and autumn gives rise to the 



12 /. e., the end nearest the micropyle. 



13 Frequently not well developed at this time. 



