44 Penhallow . — N ematophy ton Ortoni , //. 
septa in the similar hyphae of N. Logani , as determined by 
Mr. Barber 1 , would seem to indicate the possibility of their 
presence in this case. In no instance do these hyphae appear 
to cling to the walls of the large tubes of the medulla as in 
N. Storriei , but they fill isolated cavities which, for want of 
a better term, I may designate as the medullary spots. These 
spots exhibit the same general form and dimensions in all 
planes of section, and on smoothly cut surfaces of the hand- 
specimen they often appear as small cavities about i*o mm. 
broad, frequently containing minute crystals. We thus have 
evidence that these spots are not always occupied by small 
hyphae, a fact which suggests either (i) that the spaces are 
normal, and the hyphae intrusive growths, or (2) that the 
small hyphae are normal, and in some cases have been 
removed by decay or other causes. Which of these views 
is correct our material does not permit me to say ; but the 
view advanced by Mr. Barber, and strengthened by our know- 
ledge of similar openings in the various known species of 
Nematophyton , that these spaces have some connexion with 
the aeration of the plant 2 , would seem to offer a reasonable 
explanation of their occurrence. It may also be pointed out 
that the most marked alterations of structure, through decay (?) 
and crystallization, to be met with in the present species are 
found in the hyphae of these areas. With respect to the 
occurrence of these medullary spots, the present species ap- 
proaches somewhat closely to N. crassum. 
In longitudinal section it is wholly unnecessary to dis- 
tinguish between the radial and tangential planes, since the 
structure presents the same aspects in each case. The struc- 
ture consists of broad, tubular cells running in a direction 
generally parallel to the axis of growth, together with others 
less numerous, but yet in large numbers, traversing the stem 
in all directions, so that unlike the species hitherto described, 
there is a want of definiteness in direction. Occasionally 
these cells are exposed to a great length, but more commonly 
the plane of section cuts them off at frequent intervals so 
1 Ann. Bot. VI. 333. 2 Ann. Bot. VI. 337. 
