Aveust 30, 1918] 
Professor Rock has given us descriptions of 
the ornamental trees and also of many of the 
larger and more showy shrubs. The trees are 
arranged in natural sequence beginning with 
eyeads and pines, and ending with IJzxora 
(Rubiacez). 
Probably the most striking street trees in 
midsummer are two species of Cassia, C. 
fistula, the golden shower, and C. nodosa, the 
pink shower. The golden shower (plate 43) 
has long racemes of golden yellow flowers fol- 
lowed by cylindrie woody pods, 20 to 30 inches 
in length, straight and smooth like a musician’s 
baton. The pink shower (plate 44) has dense 
racemes of pink and white flowers, a gorgeous 
sight when in full bloom in June. There is a 
colored plate of this in Mr. Rock’s book. 
Another showy tree is the flame tree, Delonix 
regia (Poinciana regia) (plate 45). This is 
frequently planted in south Florida, where it 
is called royal poinciana. The large bright 
searlet flowers are in large terminal racemes. 
The visitor to the Hawaiian Islands is at 
once impressed with the number and beauty of 
the varieties and hybrids of Hibiscus rosa- 
sinensis (page 137). In this country the spe- 
cies is sometimes called rose of China. In 
Honolulu the hibiscus is commonly used as a 
hedge plant, the large red or white flowers be- 
ing conspicuous throughout the summer. 
Another common hedge plant is a species of 
the Aralia family (Nothopanax guilfoylez) 
(page 168). This does not flower in Honolulu, 
but the white-bordered compound leaves are 
attractive. The crotons (Codiwum variega- 
tum) (page 128) are common in Honolulu as 
they are in all warm countries. The narrow 
leaves are variegated with white and red, in 
some varieties strongly spirally twisted. 
The pepper tree (Schinus molle) (page 132), 
with feathery drooping foliage and racemes of 
small red berries, is extensively planted. The 
plumeria or graveyard flower (Plumiera acu- 
tifolia) (page 175), with thick stubby 
branches, milky juice and white or yellow frag- 
rant flowers, is commonly planted around 
cemeteries. The flowers are much used for the 
familiar Hawaiian leis or wreaths made by 
stringing the corollas on a thread. 
SCIENCE 
225 
One of the most beautifully shaped trees of 
the parks is the rain-tree or monkey-pod 
(Samanea saman) (plate 38). The crown is 
slightly convex and very wide spread. Another 
member of the Leguminose is the now thor- 
oughly naturalized algaroba (Prosopis juli- 
flora) (plate 36). This tropical American tree 
is now common in a belt along the shore of all 
the islands. The pods furnish an excellent 
feed for stock and the flowers furnish honey. 
It is often planted along streets. 
Professor Rock has devoted considerable 
space to the palms, of which many species are 
cultivated in the parks and gardens through- 
out the islands. To this group 23 plates are de- 
voted. The commonest and probably the most 
beautiful of the palms is the royal palm 
(Oreodoxa regia) (plate 19), the smooth white 
trunk being very attractive especially when 
the plants are growing along driveways. The 
date palm (Phenix dactylifera) (plate 3) is 
frequent, and the oil palm (Hl@is guineensis) 
(plate 22) is not uncommon. The fish-tail 
palm (Caryota urens) (plate 16) is conspicu- 
ous because of the great drooping masses of 
flowers and fruit; the betel palm, because of 
the tall and very slender stem. Our California 
fan palm (Washingtonia filifera) (plate 10) is 
rather frequent. 
The visitor to the Hawaiian Islands will find 
the book very helpful in identifying the culti- 
vated trees. The plates are from excellent 
photographs and the descriptions give just that 
information that one wishes to know. 
A. S. Hironcock 
U. S. DEPARTMENT OF AGRICULTURE 
SPECIAL ARTICLES 
A COMPARISON OF THE RESPONSES OF ANI- 
MALS IN GRADIENTS OF ENVIRONMENTAL 
FACTORS WITH PARTICULAR REFERENCE 
TO THE METHOD OF REACTION OF 
REPRESENTATIVES OF THE VARIOUS 
GROUPS FROM PROTOZOA TO 
MAMMALS" 
Tue behavior of animals in gradients of 
intensity of stimuli has long been studied. 
1 Contribution from the Zoological Laboratory, 
University of Illinois, No, 120. 
