88 



Science of Plant Life 



help us in answering this inquiry : young tissue is very tender, 

 and easily broken, while old tissue is stronger and firmer. 



Fern leaves grow at the 

 apex. The fern leaf is one 

 that may be studied in this 

 connection, for the growing 

 portion is not only tender 

 but coiled up, and its unfold- 

 ing may be noted from day 

 to day by marking with India 

 ink the successive positions 

 of the coil. In the Boston 

 fern, which is so commonly cul- 

 tivated as a window plant, the 

 leaf may continue to unfold 

 for weeks, if the water supply 

 is adequate and other condi- 

 tions are favorable. Evidently 

 in the ferns the growing region 

 is at the apex and the oldest 

 part of the leaf is the base. 

 Growth in the leaves of seed plants. The flowering plants 

 have either parallel-veined leaves or net-veined leaves, and 

 the place of growth in these two types of leaves is different. 

 In parallel- veined leaves, like those of the members of the 

 grass family, the growth is at the base. What boy or girl, 

 walking through a field of timothy or wheat, has not pulled 

 the leaves from the stems? The leaves always break near 

 the base. If you have tasted the broken end, you will recall 

 that it was sweet and tender. The breaking near the base, 

 and the sweetness there^ indicate that the growing region of 



Fig. 52. Growing regions (shaded por- 

 tions) of leaves: A, leaf of fern; B, grass 

 leaf ; and C, leaf of sunflower. 



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