328 BOTANICAL GAZETTE [OCTOBER 
The four articles reviewed indicate that cohesive stretching of water is of 
great significance in plants. They show the magnitude of force thus available 
for work and give much insight into the conditions under which it is operative; 
also they add evidence for the cohesion theory of the rise of sap. 
OPELAND® has devised a very simple but ingenious piece of apparatus 
for determining various facts concerning the movement of water through 
stems of lianas. From his measurements he concludes that the resistance 
offered by stems to water flow through them is very much less than claimed 
by other workers in this field; that the tension in the water column of the stem 
assumed by the cohesion theory does not exist; and that the living cells along 
the stem play no essential part in the movement of the water through it. 
COPELAND believes that the main problem of rise of sap remains, as he earlier 
stated,’ ““‘Why is this atmospheric pressure exhausted so slowly with the 
ascent of the tree that whatever height is reached, and however rapidly and 
forcibly water may be drawn from the wood, some pressure always remains ?” 
Notwithstanding the ingenious character of these experiments and the sug- 
gestiveness of the results, much more work of an analytical sort is needed to 
establish a new theory of the rise of sap or to dispose entirely of the cohesion 
theory.—WiLt1AM CROCKER. 
Structure of the Boleti—Very few studies on the finer structural details 
of the Boleti have been published. These have been fragmentary observations 
occasionally employed to supplement specific diagnoses drawn from the grosser 
eatures, or to interpret certain surface characters. A comparative study of 
the structure of all parts of the plant in a large number of species is greatly 
presented by YarTeEs” in the study of 6 Californian species, supplemented by 
two eastern ones. 
In general, there is not such a marked differentiation of the tissues, when 
the size of the plants is considered, as one might expect who has not given 
some attention to these plants. According to the author’s interpretation, the 
tissues of the pileus and stipe are differentiated into two main zones: an outer, 
the cortex (“rind”’); and an inner, the trama (“‘context’’). In some species the 
cortex of the pileus consists of elongate vertical hyphae, which in dry species 
give the pileus a tomentose appearance, as in Boletus chrysenteron. In the viscid 
species the outer layer of the walls of these hyphae is more or less gelatinized 
and the pileus is not tomentose, as in B. granulatus, B. luteus, and B. cali- 
® CopeLanp, E. B., Uber das Saftsteigen. Jahrb. Wiss. Bot. 56:447-459- 1915- 
PFEFFER’S Zeitschrift. 
9 COPELAND, E. B., Bot. Gaz. 34:161-193, 260-283. 19 
» VYares, H. S,, The comparative histology of certain pea Boletaceae. 
Univ. Calif. Publ. Bot. 6:221-274. pls. 21-25. 1916. 
