1897.] NATURAL SCIENCES OF PHILADELPHIA. 19-% 



istic will be irretrievably lost. But the careful student of nature 

 knows that this is not so. The seed collector goes into a wood 

 which may contain White Oak, Black Oak, Scarlet Oak, Red Oak, 

 Chestnut Oak, Swamp White Oak, Post Oak, Black-jack Oak, 

 Scrub Oak, as he may do along the Wissahickon, gather the acorns 

 of each species under its particular representative, and plant them 

 with the absolute certainty that they will be true to their several 

 parentages. This could not be if the hypothetical proposition cited, 

 of free inter-pollination, were an actual fact. 



How, then, are we to account for the striking deviations from 

 typical forms which we occasionally see? I have long believed «that 

 form is the result of various degrees of rhythmic growth. It is the 

 mechanical result of varying degrees of energy. These results may 

 be noted on a single tree. On the weaker branches of a white oak 

 the leaves will be comparatively entire ; on the stronger shoots, 

 where growth-energy is rampant, the leaves will be deeply lobed. 

 In mulberries these differences must be well known. The leaves 

 on branches full of growth-vigor are lobed, but when this energy is 

 somewhat spent, wholly entire leaves follow. Surely these facts 

 must have come within the range of common observation. 



But varying degrees of rhythmic growth may not always result 

 in lobed leaves in its aspects of vigorous growth, or of entire leaves 

 in its weaker ones, because other factors interfere. We may not 

 kuow just what these incidental forces are, though we may feel sure 

 they exist. For instance, on the common red cedar we may note two 

 distinct forms of foliage: on the weaker, half-starved branches the 

 leaves are like needles and resemble those of the common juniper, 

 but on the more vigorous branches there are seemingly no leaves at 

 all ! We have to say " seemingly," for indeed there are really leaves, 

 as really so as on the weaker ones, but the peculiar growth-energy of 

 these more vigorous branches causes them to become connate with 

 the stems. On a branch a year or two old, we can easily separate 

 these connate leaves from the true bark formed beneath. 



But that there is no necessity for bringing in hybridity to account 

 for the occasional aberrations from the normal form we meet with 

 is well known to those nurserymen whose business it is to raise trees 

 in great quantities. There are just as many and just as striking 

 variations among genera consisting of a single species, or of species 

 wholly isolated from other species of the genus, as where there are 

 several. The European Oak, Ash, Linden, Beech and many others 



