GLOSSARY 191 



Spore. A single cell (generally protected by a cell wall) which has the 

 power of germinating and reproducing the plant of which it is the 

 reproductive body. See p. 75. 



Sporophyll. A leaf or part of a leaf which bears spores or seeds, 

 and which may be much or little modified. 



Stele. A strand of vascular tissue completely enclosed in an endo- 

 dermis. See p. 62. 



Stigma. A special protuberance of the carpel in flowering plants 

 which catches the pollen grains. 



Stomates. Breathing pores in the epidermis, which form as a space 

 between two curved liplike cells. See fig. 23, p. 54. 



Tetrads. Groups of four cells which develop by the division of a 

 single cell called the "mother cell". Spores and pollen grains 

 are nearly always formed in this way. See p. 75. 



Tracheid. A cell specially modified for conducting or storing of 

 water, often much elongated. The long wood cells of Ferns and 

 Gymnosperms are tracheids. 



Underclay. The fine clay found immediately below some coal 

 seams. See p. 24. 



Vascular Tissue. The elongated cells which are specialized for 

 conduction of water and semifluid foodstuffs. 



