2 
Igor | CURRENT LITERATURE 225 
are no threads in the external walls of the epidermis, and but very few con- 
necting the guard cells with their neighbors. 
All parenchyma cells show a general resemblance in the character of 
their threads, the threads on the end walls being irregularly scattered, while 
_ on the side walls they are grouped. In the phloem all the sieve tube threads 
show a characteristic median dot. The albuminous cells at the edge of the 
phloem of the leaf have their threads grouped in localized thickenings on 
the walls, and serve to pass materials from the mesophyll to the phloem. 
The very numerous threads of the root cap form a connection with the free 
surface of the root and with the periblem. 
In the mature tissue of /. s¢/vestris the threads in the cortical tissue are 
similar to those of the seedling. In the phloem there is no connection 
between the sieve tubes and the bast parenchyma or the starch medullary 
ray cells. The sieve tube threads on the radial walls have a median dot. 
The torus of the bordered pit is probably traversed by threads which soon 
disappear. In the leaf, the distribution is about the same as in the cotyledon. 
The endodermis, with very numerous threads, is in close connection with the 
cortex and the stele. In the pericycle, living cells are connected by threads, 
but there is no connection between the pericycle and the lignified transfusion 
tissue. 
In general, the main direction of threads in the cortex and phloem is 
tangential. The transitory nature of certain threads explains the absence of 
threads between the sieve tubes and medullary ray cells. Except in the 
medullary rays and in the cork cambium, the threads are chiefly on the 
radial walls. This suggests that in conifers food supplies and stimuli are 
conducted mostly in a tangential and vertical direction.—CHartes J. 
CHAMBERLAIN, 
