Manchester Memoirs, Vol. lix. (191 5), No. 3. 17 



but also between the root-bearing and leaf-bearing regions 

 of the cortex. Since the plane of section follows approxi- 

 mately the line of the future split, it may show the tips 

 of young roots belonging to both sides of the rhizophore 

 {cf. Fig. 3 B). The arrangement and succession of roots 

 will not be dealt with here, but it may be noted in passing 

 that a strict arrangement in vertical lines, the youngest 

 roots being nearest the stem apex, is not self-evident. 

 This question will require careful consideration, but the 

 succession in vertical series (which is often more apparent 

 than in these sections) is mentioned here, since, if estab- 

 lished, it is one of the difficulties in recognising the lower 

 growing line as the correlative of the shoot apex. 



In the stock represented in Fig. 4 B, the widening of 

 the rhizophoric stele has been allowed for by the develop- 

 ment of secondary tissue around the base of the stem 

 stele (and partly by the stretching and disorganisation of 

 the narrow basal region of the latter), but the secondary 

 meristem has not contributed to the extension of the 

 growing line itself On the other hand, in stocks like 

 Fig. 4 A y with which Fig. 2 may be compared, the rhizo- 

 phoric region of the stele is continued upwards parallel to 

 the lower part of the stem stele, and this extension 

 appears to be due to the meristem of the stem contributing 

 to the increase of length of the lower growing line and 

 altering its behaviour accordingly. This, while not proving 

 the rhizophoric region to be merely a peculiar secondary 

 growth, indicates the close relation between the deep- 

 seated growing line of the rhizophoric region and the 

 secondary meristem. 



All the plants hitherto considered are of the usual 

 type found in full grown plants in having a secondary 

 zone of prismatic tissue, developed within a cambium, 

 around the older portions of both stem stele and rhizo- 



