1900] OBSERVATIONS ON LESSONTIA 331 
respects resemble the true sieve-tubes in form, There seems to 
be the same evidence of passive elongation and occasional 
obliteration that was noted in Nereocystis, and the same frag- 
mentation of nuclei no doubt initiates the process of elongation. 
Upon the comparison of Lessonia with Nereocystis, it would 
seem reasonable to describe the “true sieve-tubes”’ of Wille and 
Oliver as modified sclerenchymatous elements of the perimedul- 
lary cortex, 
The splitting of the lamina has not been definitely studied in 
this material, but so far as can be judged from the observations 
that have been made it takes place in the same manner as pre- 
viously described for Nereocystis. 
The lamina.— The essential structural basis of the lamina and 
me arrangement of the tissues indicate its complete morpholog- 
al equivalence to the stipe. The pith is of course greatly 
extended into a narrow ribbon, the cells of which while retaining 
the web structure are not conspicuous for granular contents, 
indicating that the stipe serves in some sense as a reserve organ, 
Maile the leaf, essentially photosynthetic, uses its pith more 
Particularly as strengthening tissue and a conduction path. On 
ag of the ribbon-shaped pith parenchymal’ tissue - 
“Yeloped outside of a narrow intervening layer of sclerenchyma. 
pil the epidermis chlorenchyma cells extend, ares 
of the S layers. The epidermal cells are not so low as a 
“a stipe, but generally show a long diameter perye ag 
ing - the surface of the lamina. A well marked cuticle a0 
- ee 1s uniformly present. The edges of the epee 
to the aad ae (belonging in part to the pith a a oe 
give stre ex) with small diameter and thick we s, ete 
‘ ves it is probable tha 
ae gth to the margin. In younglea 
ance of b — is not immediately differentiated. bei noe 
ae . midribis caused simply by the greater hi 
. ed the central portion of the lamina and its . i 
th Pr thinning out at the sides. I was unable to dieteg™ : 
: ing tract any distinction between that portion which lay ™ 
midrib and the portions on either side, nor do the cortical 
