SCIENCE—ADVERTISEMENTS 
Ginkco. Maidenhair Tree. 
* (Family Ginkgoaceae). 
Gray-barked trees of rather coni> 
cal habit but usually with irregul- 
arly placed exceptionally large 
branches: deciduous. Twigs mode- 
rate, rounded, with quickly shred- 
ding outer bark: pith rather small, 
_ Somewhat 3-sided, brownish, 
spongy. Buds solitary, moderate,' 
sessile, round-ovoid or hemispher, 
ee ical, with about 3 exposed scales, 
usually developing into blunt 
Spurs. Leaf-scars alternate. crowd- 
ed on the spurs but separated else- 
where, ‘crescent-shaped or trans- 
versely elliptical, low, moderately 
small; bundle-traces 2: stipule- 
scars lacking. (Salisburia.) 
The maidenhair tree possesses 
peculiar interest as the sole rep- 
resentative of its family, and in 
being essentially a species which 
thas been preserved only through cultivation. Except for the, 
leven more primitive cycads, of which several Benera are to 
'be found in greenhouses and are used for formal effects in 
‘the warmer parts of the world, it is the only Spermatophyte 
‘which possesses ciliated male ;gametes,—a CEELERUG: common 
‘to all fernworts and mossworts. 
Winter-character references: Blakeslee & iyatvicl 333, 
'282, pl.; Bésemann, 68; Otis, 2; Schneider, f£ 57, 64; Shirasawa, 
265, pl. 9. The contrast between long shoots and spurs is 
discussed by Collins in the sixth volume of The Plant World! 
Twigs buff or gray: buds light. brown. , G. biloba.! 
TRELEASE, WINTER BOTANY 
A pocket size book of 400 pages (type-bed 34x 5 in.), well 
made, durably bound, opening flat. Keys based on simple 
winter characters lead to the names of 326 genera, illustrated 
by figures in the text, and over 1,000 species. Five contrasts 
in the general key identify the maidenhair tree with certainty, 
by use of the characters pictured above. Ready September 
30. Price $2.50 postpaid. To be had of 
WILLIAM TRELEASE, URBANA, ILL. 
JUST PUBLISHED 
Introduction to 
The Elementary Functions 
By RAYMOND BENEDICT McCLENON 
EpiTEp By 
WILLIAM JAMES RUSK, Grinnell College 
A text-book in mathematics for freshmen in 
colleges and technical schools and for advanced 
pupils in secondary schools, which includes se- 
lected subjects from trigonometry, analytic ge- 
ometry, and differential calculus. The prob- 
lems are especially well chosen; the presenta- 
tion is inductive; the style is direct and infor- 
mal. 
This book is especially timely in that with 
certain chapters as a basis shorter courses, for 
three months or for six months, can easily be 
arranged. This feature particularly adapts the 
book to S. A. T. C. and other rapid survey 
courses. 
ix-+244 pages, $1.80 
GINN AND COMPANY 
70 Fifth Avenue 
NEW YORK 
The University of California Press 
Berkeley, California 280 Madison Ave., New York 
Fundamental Equations 
of Dynamics 
And Its Main Co-ordinate Systems Vec- 
torially Treated and Illustrated 
from Rigid Dynamics 
By FREDERICK SLATE 
Professor Slate has concentrated his attention on the 
group of topics where opportunities for modification 
are plainly in evidenee, and his work demonstrates 
how our further reading of arguments and results 
may need to be cleared or rectified in its details. 
288 pages. Cloth, $2.00; Paper, $1.50. 
Carriage extra. 
List of publications sent on request 
Handy 
Resistance Units 
These are furnished in single value blocks, 
ranging from 0.1 ohm to 10,000 ohms. Blocks 
for all values are uniform in size, and can 
readily be arranged in groups to build up any 
desired resistance. Adjustment is made to 
within 1/20 of one per cent. 
We have just issued a new Circular (No. 10), 
describing and listing these units. Write 
for it. 
Circular No. ro also describes a new two-value 
Unit, especially designed for teaching purposes, 
to check up students on resistance measurements. 
PYROLECTRIC INSTRUMENT Co. 
Pyrometric and Electrical Precision Instruments 
636 EAST STATE STREET TRENTON, N. J. 
E, F, Northrup, President and Technical Adviser 
