PLANT TISSUES 115 
According to the position of the meristems in the plant, they 
may be classified as apical, intercalary and lateral. 
ApIcAL MERISTEMs consist of growth cells which occur at the 
tips of roots and stems. They produce growth in length by giving 
Thy 
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Fic. 57.—The cambium and medullary rays in tangential-longitudinal section. 
x 50. The section has been cut through the cambium zone adjacent to the 
phloem or inner bark of the stem of the tulip poptar, Liriodendron tulipifera, and shows 
besides the elongated taper-ended cambial cells, phloem parenchyma which has been 
cut off by the transverse divisions of cambial cells, also medullary rays. ca, cambial 
cell, in the upper portion of which two phloem cells have been cut off; ca’, cambial 
cell at left of which is a row of phloem parenchyma; r, medullary ray. 
rise to primary tissues. In the bryophytes and pteridophytes the 
apical cell represents apical meristem, while in spermatophytes 
a group of apical cells makes up this tissue. 
INTERCALARY MERISTEMS represent parts of apical meristems 
which have been separated*from the rest of apical meristem by 
