Growth. 23 



torn by the _jncrease in_iQlume-^ef-4h«-t^iss«es f ermed f rojtn _tJie_ 

 generative layer, or cambium. The concentric rings of wood 

 injhe stem may _be_ made J2ut_ with^Jhe_unaided_eye, jijhe. 

 surface is^airlyjinooth. One ring is_ordinarily_formed _every 

 year. If the growing season should be interrupted by ajiiid- 

 summer_drought, two _Tings__iiiight_be_jaimed_in_--a^-single 

 season. 



THe thin cylindrical sheet of cambium develops cells in its 

 inner layers, which become converted into woody tissues. The 

 tissues external to the cambium arise by various methods. 

 (For a detailed study of the characters of a woody stem see 

 Gregory, E. L., " Elements of Plant Anatomy.") 



Examine the trunk of any tree which has been recently 

 felled, or the freshly cut stump, and count the number of rings 

 of wood. ^Taking into account the exigencies of climate, the 

 age of the tree in years vHll_be_sornethingJessJhan_th£.ni^^ 

 of annual rings. Determine the height of the tree. If possi- 

 We, compare the two measurements with those obtained from 

 a second tree of the same species. 



.8. Growth of leaves with netted veins. — Select 

 some plant, such as sunflower [He/ianf/ius), dandelion (Tarax- 

 acum ) , peach (Amygdalus) , maple (Acer) , chestnut ( Castanea'), 

 or squash (Ciicurbita'), in which the young leaf as it unfolds 

 from the bud is but a fraction of its adult size. Mark off a 

 series of in tervals of '^ ^ mm. in a straight line f r om the base^ o 

 the_apeXj using a glass tube drawn to a fine point as a pen. 

 Mar k off a second series of right angles to this i n the middle 

 jof-JJieJeai. Take lengths of these intervals on successive day§ 

 until full size has been reached., A\'hat is the position of the 

 zo ne of m aximum elongation ? Does the extension of a leaf in 

 breadth co me f roni~tEe~growth of tissues near the midrib or 

 near_die-_niargin ? A\'hat is the daily rate of growth in both 

 direc^cais? ' 



g. Growth of a frond of a fern. — Select a fern with 



