Growth 319 



Halle, Germany, from October 28 to November 4, more 

 than one half, or 125 species, began to make growth 

 promptly under greenhouse conditions. Thus it is 

 apparent that a large number of deciduous trees merely 

 require favorable conditions for growth in order greatly 

 to reduce the normal rest period. 



Observation upon orchard and forest trees fully confirms 

 this view. It happens frequently in temperate regions 

 visited by drought in the early summer that the resting 

 bud is formed early, and defoliation of many of the spring 

 leaves may occur by midsummer. In such cases, a return 

 of moist weather and favorable conditions in the late 

 summer or early fall may result in a flush of growth from 

 the resting bud of the same season. Sometimes this may 

 be accompanied by fall blossoming. 



186. Differentiation of stem tissues. A complete 

 study of internal anatomy, or histology, is not the pur- 

 pose of the following paragraphs. It is, however, essen- 

 tial to note the common method of growth or develop- 

 ment of some of the 'chief tissues and tissue systems 

 within the plerome of the growing tip. There are pro- 

 duced by division and differentiation of the tip meristem 

 strands of elongated cells known as the procambium. 



In dicotyledons, these strands may be commonly 4 to 

 10; typically they are disposed as an interrupted ring in 

 the outer portion of the plerome, surrounded by cells of a 

 less differentiated meristem, often termed the ground or 

 fundamental tissue. The procambial strands become 

 by differentiation the primary fibrovascular bundles. 

 In developing the common type of bundle (collateral 

 type), the inner portion of the procambium becomes the 



