CONIFERALES (PINACEAE) 



225 



the greatest amount of work has been done in fixing juvenile forms, 

 such relatively permanent forms being known in cultivation as species 

 of Reiinospora. While some of the adult forms of Cupressineae, as 

 Juniperus communis, retain the 

 habit of spreading needles, others 

 develop concrescent leaves upon 

 their adult shoots, that is, leaves 

 whose adaxial faces have become 

 organically connected with the 

 adjacent stem surface, so that 

 they appear as green scales. In 

 such cases, the juvenile form, 

 with its spreading needle leaves, 

 presents a striking contrast with 

 the adult form (fig. 256). In 

 shoots from stumps or wounds, 

 the juvenile form of leaf has 

 been observed in Pinus, Thuja, 

 and Taxodium, a response quite 

 in harmony with Jeffrey's in- 

 terpretation of the appearance 

 of resin ducts as a traumatic 

 response. The juvenile forms 

 of Sciadopitys, like those of 

 Pinus, produce simple needle 

 leaves upon long shoots, but 

 later, scales appear instead of 

 needles, and in their axils the 

 peculiar double needle leaves are 

 developed. 



GoEBEL suggests that the 

 juvenile form prol^ably repre- 

 sents the more primitive form. 



It is certainly true that if the adult bodies of many of the forms, 

 not mentioned above, be associated with these juvenile forms, a 

 very consistent body is discovered for Pinaceae (and for Conif- 

 erales). It would follow that the replacement of fohage leaves 



Fig. 254. — Araucaria excelsa: a 

 specimen in the Washington Park 

 (Chicago) conservatory. 



