44 BOTANICAL GAZETTE funy 
sieve tube, and immediately a border to the ray is produced, with 
the erect cells as usual coterminous with marginal tracheids. 
Similar instances have been found in other species of Pinus, and the 
transition from sieve tube to erect cell is not always as abrupt as in 
the case figured. Since the cells of the radial rows are sieve tubes 
in all respects save length and the nucleus, the occasional formation 
of an erect cell by cutting off a segment from a sieve tube does not 
seem surprising. In fact it does not seem necessary to assume an 
absolutely uniform mode of ori- 
gin for the erect cells, in view 
of the fact that a certain cambial 
cell may be giving rise to ray 
tracheids, but for some reason 
suddenly cut off a parenchyma 
cell instead. Similarly a row of 
ray cells of the phloem may at 
first be albuminous, but later- 
formed members of the row may 
contain starch. We are inter- 
ested here, however, in the ques- 
tion as to the evolutionary origin 
: of the erect cells, rather than in 
Bio ok Strobus, 4-year root: occasional modes of origin. 
ends, hin a, oi oO = ents inane ‘ 
X275. ’ mation of a ray, showing the 
tendency of sieve tubes to cut 
off a cell from the end, has been observed a few times. An example 
— cena Ta a a of P. Strobus, is represented in 
z Po SO — the habit of cutting off a cell from the end of 
pet hrstaam aie so a established that a narrow ray has 
ieay ales 7 85 cambial region at the right. This process 
ema api € mode of origin of erect cells described in 
& paragraph. 
ae RE cae most on results have been obtained from a 
sae noite : . e stem of Pinus has also been examined 
eck ie, zit e mode of origin of the erect cells in this case 
pared with what may be seen in similar regions 



