Further Studies of

Ar-i Their Pollination

Ey
William T«n&3ease

UNIVERSITY OF CALIFORNIA
AT LOS ANGELES

Further Studies of Yuccas;
aod tlneir Pollination.

By WILLIAM TPELKASE.

THE FOURTH ANNUAL REPORT OF THK MISSOURI BOTANIC.U >
ISSUED, MARCH 9, 1893.

I

FURTHER STUDIES OF YUCCAS AND THEIR POLLINATION.

BY WILLIAM TRELEASE.

Among the many strange things brought to light by
biological studies, few equal in interest or verge so closely on
the improbable as those which concern the pollination of
the Yuccas. The observed facts, chiefly known through
the work of Professor Charles V. Riley and the late Dr.
George Engelmann, have been admirably summarized by
Professor Riley in the Third Report of the Garden.* So
far as direct observation on pollination is concerned, these
refer to cultivated specimens of Y. filamentosa and glauca,
the latter of which has been observed also in the wild
state in Colorado ; f but the collections of entomolo-
gists, and the affected fruits of the Yuccas of various
localities, show that virtually all species of the genus
depend for their principal pollination, if not altogether,
upon moths of the Tineid genus Pronuba, of which Riley
has characterized three species, i Professor Riley, there-
fore, states that all of the species of Yucca native east of
the Rocky Mountains depend for their pollination, so far
as is now known, upon a single species of Pronuba, namely
the white P. yuccasella ,§ while the tree Yucca of the
California desert and the adjacent region, Y. brevifolia,
is pollinated by a dingy moth, P. synthetical and the
aberrant Yucca W7iipplei, which Mr. Baker is now dis-
posed to place in a distinct genus under the name Hespero-
yucca, is pollinated by an equally aberrant spotted moth,
P. maculata^ the pollinating actions of which have been
briefly reported this season by Coquillet. * * Aside from this

* pp. 99 to 158, pi. 34 to 43. f Riley, I. c. 124. J I. c. 137.

§ I. c. 104, 121; Proc. Biological Society of Washington, vii. 94;
Insect Life, iv. 369. || I. c. 121, 141. f ?. c, 121, 139.

** Insect Life, iv. 370, note.

[181]

252974

182 MISSOURI BOTANICAL GARDEN.

nothing definite has been made known concerning either the
Pronubas which frequent the several species of Yucca, or
their mode of operation, although Riley predicts the prob-
able discovery of distinct species of Prontiba for the Mexican
Y. jilifera* and our own Y. rupicola,] Y. Treculeana^
and Y. baccata.\

The following pages contain the results of a further field
study which I have been enabled to make during the spring
of 1892, through the interest of the Board of Trustees of
the Garden. In bringing the observations together, they
have been arranged under the respective species studied, the
classification of the latter being substantially that employed
in the detail illustrations of the last volume. §

YUCCA.

Filaments nearly or quite free from the petals; pollen powdery ; style
stout, not capitately expanded nor long-papillate, with a rather open stig-
matic axile canal; fruit baccate, spongy, or capsular with septicidal and
apical-loculicidal dehiscence.

A. SARCOYUCCA, with fleshy fruits.

r. ALOIFOLIA, L. (PL 18).— According to Riley, || in-
dividuals of this species which bloom simultaneously with
Y. filamentosa along the southeastern coast, are pollinated
by Pronuba yuccasella. The species is, however, quite
unique in setting good fruit rather abundantly in cultiva-
tion when Pronuba does not appear to be present. If This
was the case in the Garden this year, when the species

* L c. 131. f I. c. 122. J Proc. Biol. Soc. Washn. vii. 96.

I Third Report Mo. Bot. Garden, 161. || i. c. 121.

f The principal references to the fruiting of aloifolia without Pronuba
are the following: Deleuil, Rev. Horticole.-abst. in Gard. Chron. 1880.
siii. 807; Engelmann, Gard. Chron. 1872,941, Collected Writings, 284 ;
The Garden, fide Tick's Mag. 1880 and Riley in Proc. Amer. Ass. Adv.
Sci. xxix. 624; Gardeners' Chronicle, 1880, xiii. 81; Riley, Third Garden
Report, 118 etc.; J. v. V. [van Volxem], Gard. Chron. 1882, xviii. 407.
The note of Layard in Nature, xxii. 606, may perhaps refer to this
species, though the species is not named.

FURTHER STUDIES OF YUCCAS. 183

bloomed for the first time in several seasons, and a number
of the panicles fruited quite freely. The earliest of these
flowers opened as the last flowers of filamentosa were fall-
ing, so that it was supposed at first that they were pollin-
ated by P. yuccasella, which had been observed only a few
days previously, but this supposition was not substantiated
by the discovery of the moth about them, or of its larvae in
the fruit.

Professor Kiley has shown that the short style and open
stigma of aloifolia appear to favor self-pollination when the
moth is not present ; but a study of our plants this summer
by Mr. Webber and myself has not satisfied either of us
that self pollination is likely to occur sufliciently frequently
to explain the rather abundant fruiting observed here, and
in the case of a single panicle covered with gauze, no fruit
was set except as the result of artificial pollination. The
so-called Yucca hybrids of gardens appear for the most
part if not always to be spontaneous or artificial crosses
between the variegated and other forms cultivated under
various names, but now generally referred to this species.
Altogether Y. aloifolia is one of the species most worthy
of study in its native habitat, since little is known except
that it sometimes fruits without the aid of Pronuba, and
that its seeds sometimes contain the larvae of P. yuccasetta,
while the exact mode of pollination when the moth is
excluded is not known from observation.

It is well known that filamentosa, when cultivated far
north of its range, is uncertain in its blooming, although
further south it flowers every year ; and attention has been
called frequently to the periodicity of brevifolia and other
species in their native home.* No doubt this is connected
with the previous conditions of nutrition, and the im-
mediate climatic influences under which the plants have
grown, but it appears quite remarkable that so many plants
of aloifolia at the Garden, of very different size and age,

Riley, L c. 117.

jg4 MISSOURI BOTANICAL GARDEN.

should have bloomed together this year, after a long period
of rest.*

The most striking morphological peculiarities of the
species, aside from its rather stiff sword-shaped denticulate
leaves, are the marked stipe of the ovary, and the decidedly
hexagonal cross section of the ripening fruit, due to the
rapid growth of the nectar grooves, — both of which feat-
ures are well shown on plate 44 of the Third Report.

Y. YUCATANA, Engelm. — So far as I can learn, nothing
is known of this species further than that it was collected
in Yucatan by Schott, whose specimens are preserved in a
few herbaria.

Y. GUATEMALENSIS, Baker (PI. 1, 2, 19). — This species is
said to occur in southern Mexico, as well as Guatemala.
In August and September, 1892, a fine plant, said to have
come originally from Haage and Schmidt as a Furcroea,
bloomed in the Garden, synchronously with a form of
gloriosa, but fully a month later than aloifolia. The polli-
nation arrangements appear to be almost identical with those
of baccata, which are described below. In this specimen the
scptal nectar glands, although they are not very large, were
more active than those of any other true Yucca known to
me, and their secretion appeared in rather copious drops at
the base of the ovary, where the nectar grooves open, or
in smaller drops near its top, where the glands open into
the grooves, if, as frequently happens, the latter have
spread somewhat. Artificial pollination gave a number of the
very large pendent baccate fruits, but nothing is known of
the natural pollinators of the species.

The fruit raised by artificial pollination is very stout.
One of the larger (but not the largest) of the specimens
measured 2X3£ in. and weighed, while still green, 6 oz.
At first quite hexagonal in cross section, its intercarpellary
facets ultimately disappear toward the base. The bases of
the filaments are adherent to the base of the fruit, much

* Meehan (Monthly, ii. 190) mentions a plant which flowered for the
first time when at least seventy-five years old.

FURTHER STUDIES OF YUCCAS. 185

as in aloi folia, and similarly reflexed. When fully grown,
but not ripe, the fruit is of a clear apple-green color.

Y. SCHOTTII, Engelm. ( Y. macrocarpa, Engelin.) (PI.
3). — Though Y. macrocarpa , which appears to be only
this species, is not uncommon in parts of southern Arizona,
no observations have been made on its pollination, and I
was unable to find it in bloom. Flowers collected in the
Santa Kita Mountains, July 9, 1881, and in the Huachuca
Mountains in September, 1882, show either an unusual dura-
tion of the flowering period, or great variability in it.
Y. elata and Y. baccata, which are spring-blooming species
of the same region, are pollinated by Pronuba yuccasella,
which can scarcely be expected to occur as late as the dates
mentioned; but baccata, in different localities, is known to
have a prolonged period of blossoming comparable with
that of the different forms of filamentosa in the southeast,
so that it is possible that in its pollination arrangements
Schottii bears the same relation to baccata that the autum-
nal gloriosa does to filamentosa .

Y. TRECULEANA, Carr. (PI. 18).— This Texan and
Mexican species is believed by Riley to be pollinated by a
probably distinct Pronuba,* but no observations have been
made on it. A specimen which bloomed in the Garden this
season was quite as sterile as other cultivated Yuccas aside
from filamentosa and glauca, which are pollinated by
P. yuccasella, and the aloifolia noted above; and this
has been the case on the several occasions when the speci-
men has bloomed in the past.

According to Engelmann f Treculeana is reported by
Lindheimer as sterile in Texan gardens, though the wild
plants are abundantly fertile.

Y. BACCATA, Torr. (PI. 20). — With the possible exception
of Y. glauca, this is the most widely distributed of
our species, ranging in a variety of forms from southern
Colorado into Mexico and to California, where it extends

* I.e. 122; Proc. Biol. Soc. Washn. vii. 96; Insect Life, iv. 371.
t Collected Writings, 284.

186 MISSOURI BOTANICAL GARDEN.

from about Monterey into the peninsula. It therefore
connects the territory of glauca, which is pollinated by
Pronuba yuccasetta, with that of two Calif ornian species
pollinated by very distinct moths. No observations appear
to have been made heretofore on its pollination, nor has
any Pronuba been taken on its flowers, but Professor Riley
predicts the probable discovery of a distinct species for it.*
In the valley between San Bernardino and Colton, Cali-
fornia, baccafa is found in some abundance, but no Pronuba
Avas seen in any of the specimens examined about the mid-
dle of April, when they were in full bloom, and they are
said never or very rarely to fruit there, by Mr. S. B. Parish,
in whose company my observations on this occasion were
made.

About Banning and Cabazon, on the western edge of the
Colorado desert, where the plants are more abundant and
of larger size, often with a trunk five or six feet high,
they are more generally fertile, and a quantity of fruits of
the preceding year were collected from the crowns of
leaves into which they had fallen on maturity, and where
they had been protected from rodents. Most of these
fruits were strongly constricted about the middle, and per-
forated in places, where the larvae of a Pronuba had
escaped. The plants were not blooming very freely this
year, but several specimens of a white Pronuba were taken
resting in the flowers, and though numerous panicles had
bloomed without setting any fruit, others were sparingly,
and still others abundantly, fertilized, and the ovaries of
the fertilized flowers showed unmistakable constrictions or
indentations indicative of the opposition of Pronuba; still,
the moths were not sufficiently numerous to render night
observations on their work possible.

A number of blooming plants of baccata were examined
about the first of May on the mesas back of San Diego,
where, notwithstanding the more southern latitude, the

* Proc. Biol. Soc. Washington, vii. 96.

FURTHER STUDIES OF YUCCAS. 187

season is later than on the desert and in the warmer valleys
further north. On this occasion I was accompanied by Mr.
C. R. Orcutt, who informs me that the seeds of baccata are
in some seasons very much eaten by larvae, probably of
Pronuba ; * and the cluster of perforated fruits figured on
the accompanying plate was photographed many years ago
in the same region. Though the oldest pistils were less
developed here that at Cabazon, there was abundant evi-
dence that they had been oviposited in by Pronuba,
several individuals of which were taken in the flowers.

The flowers of this Yucca, though they are as variable
in form as those of the eastern capsular species, agree, so
far as I have observed, in having the sepals decidedly um-
bonate at the base, as is also frequently the case with
aloifolia, so that each flower appears somewhat as if con-
stricted immediately above the bottom. In color they
range from creamy white, often with a tinge of green, to a
decided brown purple, the perianth being always very glossy,
and they are slightly and delicately fragrant. The mi-
nutely papillate filaments vary much in length, but com-
monly reach to about the base of the style, where they are
more or less abruptly thickened and bent outwards. In
one observed case, however, they were as long as the entire
pistil. A curious feature observed in dried specimens as
well as in recently fertilized flowers with drying stamens,
is the strong recurving of the upper part of the filaments
shown on plate 48 of the last Report, but never observed
in fresh unfertilized flowers, as it of ten is in Y. Treculeana.

The anthers do not appear to dehisce quite as promptly
as in the filamentosa group, where there is practically no
dichogamy, so that in this species the Pronuba is more
likely of necessity to have derived her load of pollen from
another flower when she begins pollination on one which is
newly expanded ; but the protogyny noted scarcely extends
beyond the evening on which the flower opens, so that it is

* Specimens of old fruit received since the above was written are
badly infested by an undetermined beetle.

138 MISSOURI BOTANICAL GARDEN.

by no means as effective in preventing close fertilization as
in brevijotia and Whipplei, which are described below.
The bright golden yellow pollen is readily seen on any part
of the flower in contact with which it may have come, and
particularly, on the nearly white ovary and the pure white
style.

The latter is not usually as long as in the flower figured
in the last Report and already referred to. It has a very
open stigmatic tube which passes into the upper ends of the
ovarian cells, as may be seen in some cases even by looking
down the wide channel with the aid of a hand lens, for there
is little stigmatic secretion. In this species it is also very
easy to convince oneself that the three pollen-conducting
grooves, similar to those figured by Webber for glauca*
but also seen in Agave and other plants with this type
of pistil, are formed by the uppermost part of the infolded
edges of the carpels, which further down coalesce to form
the true septa, and constitute the placentae. As in other
Yuccas, each septum of the ovary contains a nectar gland ;t
but the glands of baccata are not so large and open as in
the Jilamentosa group of species, in this respect agree-
ing with those of the other fleshy-fruited Yuccas that I
have examined. Notwithstanding this, they appear to be
rather more active than in the former group (herein
agreeing with Guatemalensis among the baccate species,
gloriosa among the spongy-fruited species, and the Hespero-
yuccas), their secretion sometimes appearing in small
quantity at the base of the pistil, where their large ducts dis-
charge. Several of the flowers examined at San Diego in
the morning were very wet on the outside, a condition which
has been observed on other species ;J but though it is

* American Naturalist, 1892, 303, 309, pi. 13, f. 38.

t Trelease: Bulletin of the Torrey Bot. Club, 1886, 135, and Third Gar-
den Report, pi. 63; Riley, L c. 109, Proc. Biol. Soc. Washington, vii. 91,
and Insect Life, iv. 364 to 366.

J Y.ftlamentosa,— Meehan, Proc. Phila. Acad. 1888, 276, and Trelease,
Third Garden Report, 123 ; Y. gloriosa,— Meehan, Proc. Phila. Acad. 1880,
355, 1883, 191 ; and Hesperoyucca, mentioned below.

FURTHER STUDIES OF YUCCAS. 189

pretty clear that this fluid is not derived from the septal
glands, its source is not evident.

A number of small beetles and flies visit the flowers,
apparently attracted by the pollen, which in some cases
they have been seen to eat. As was noted last year for
glauca* these insects sometimes dislodge masses of
pollen from the anthers, and the length of the stamens in
baccata may frequently cause some of this to fall upon the
tips of the stigmatic lobes. In one case a small mass of
pollen was found in this position, and, in another, some
pollen had been pushed into the mouth of the stigmatic
chamber, evidently having fallen upon the petals and been
transferred to the stigma by the pressure of my hand as I
gathered the flower. In some such way, therefore, perhaps
exceptional pollination may be effected now and then in
baccata when Pronuba is not present ; but I should not ex-
pect this to be of frequent occurrence, and the observations
at Colton show that it must be rare or ineffective.

The moths taken in the flowers of this species at Cabazon
and San Diego are somewhat larger than many specimens
of Pronuba yuccasella, and they appear to have the tip of
the abdomen, the maxillary palpi, and the antennae, as well
as the chitinized parts in general when denuded, a little
darker in color, but aside from these and the greater ease
with which their scales are rubbed off, I can detect no
characters by which they can satisfactorily be separated
from P. yuccasella of the Mississippi Valley and Rocky
Mountains, which is also said to be indistinguishable from
the moth of the Gulf region. f Like the eastern representa-
tives of yuccasella they rest within the flowers during the
day, with their heads directed toward the base of the
stamens, though they seem a little more ready to drop from
the flowers when disturbed. Unfortunately I have been
able to make no observations on their work, but the
females bear loads of pollen of the usual form, and fertil-

* Cf. Riley, I. c. 125.

t Professor Riley has since confirmed this conclusion.

jg0 MISSOURI BOTANICAL GARDEN.

ized flowers show conclusively that they thrust this well
into the stigmatic canal, — in some cases apparently even
into the top of the ovarian cells, which, owing to the short
style and the deep stigmatic notches, they can reach easily
with their long maxillary tentacles. In ovipositing, they
doubtless back down between the upper ends of the
stamens, and the ovary is pierced at about its middle. The
septa, and the median line of each cell (which is produced
into the cell as a false dissepiment, dividing the cell into
two), being covered by the appressed lower part of the fila-
ment, the moth is constrained to puncture the wall part
way between the true and false partitions, as she commonly
does in filamentosa,* this being also its thinnest part. At
San Diego, where the moths were more abundant than at
Banning, as many as three to five punctures in a vertical
series were seen several times in one cell of an ovary, the
other cells sometimes showing none at all.

The compound microscope reveals the presence of pollen
in the stigmas of all such flowers punctured for oviposition
as I have examined, and a hand lens commonly shows it,
though not always. The open stylar canal is frequented
by large numbers of a white Thrips, which sometimes pene-
trate into the cells of the ovary, and doubtless scatter
the pollen greatly, perhaps devouring some of it. On dried
fruits of the preceding season, the perforations made by
escaping larvae are commonly elevated, the uninjured tissue
evidently shrinking more in drying than that immediately
surrounding the tunnel of the larva. These dried fruits
sometimes show constrictions corresponding to the points
of oviposition, but they are frequently obliterated in the
development of the pulpy exocarp.

Y. AUSTRALIS, (Engelm.). (PI. 4, 5). — A study of
material on the Sierra Blanca plateau of southwestern
Texas, and a careful review of the literature of the species
related to baccata, enables me to fix without further ques-

* Riley, 1. c. pi. 36, f. 2.

FURTHER STUDIES OF YUCCAS. 191

tion the namej£Zt/§ra for the large Mexican " palma " with
drooping panicle, for it has satisfied me that the greater
part of Engelmann's Yucca baccata, var. australis consists
of another form (from which perhaps one other species with
erect panicle, in the upper Mexican plateau, may be sepa-
rated ultimately). Y. australis is the large Yucca
collected by Thurber about Parras, Coahuila, in November,
1852 (no. 1857, in Herb. Torrey.),* and said to become
sometimes thirty feet high and two or three feet in
diameter, by Bartlett,f who figures a much branched large
specimen. It is also mentioned by Baker in the Gar-
deners' Chronicle for 1870, p. 1088, under the number
26, but without name; and by Engelmann (cf. Col-
lected Writings, p. 292), as a variety under baccata. So
far as I can judge from herbarium material, it was
collected in Mexico by Coulter (no. 1571 in Hb. Gray.),
and it appears to be the plant collected in the Carneros
Pass, Coahuila, by Pringle in 1889 (no. 2841 ) and 1891 (no.
3912). It appears, therefore, to be a species of the
northern high lands of Mexico, extending into the elevated
Sierra Blanca region of Texas, where it is associated with
other southern plants like Agave applanata and A. Posel-
gerii. Its nearest described allies, which Mr. Baker tells
me have narrow leaves, are Y. periculosa, Baker, and Y.
circinata, Baker, both of which, like the present species,
have been referred usually to baccata, and which are yet
imperfectly known.

Seedling plants have the blue-green leaves of Treculeana,
and possess a cluster of rather fleshy fusiform roots be-
coming as thick as one's finger, but no central tap root.
With age these roots are replaced by long, tough, cord-like
roots as thick as a lead pencil. The trunks at length be-
come a foot or two thick, and generally from ten to fifteen
feet high, where my observations were made. Though

* Torrey, Bot. Mex. Bound. 221-2.
t Personal Narrative, ii. 490.

192 MISSOURI BOTANICAL GARDEN.

commonly unbranched or with only a double crown, they
sometimes develop several large, more or less spreading
branches. The very concave leaves are of a clear green
color, and either entirely smooth to the touch or only
slightly scabrous on the few angles which sometimes run
longitudinally on the back. Their margin on unfolding is
entire, purplish brown, and dilates into the firm but blunt
brown tip, from which, after the leaves have expanded, it
breaks away in the form of numerous stout gray or brown-
ish fibers, pectinately spreading near the apex, and becom-
ing longer and more remote below, so that ultimately the
leaves are not filif erous except for a few crowded short fibers
immediately below the point, and a more or less abundant
aggregation of loose threads between their bases, causing a
cobwebby appearance. The older leaves for a long time are
reflexed against the trunk, and appear to be more fibrous
and rigid than those of Schottii and baccata. The inflores-
cence is ample, recalling that of Treculeana, and the con-
spicuous white bracts sometimes measure as much as 3X12
inches.

In the Texan region indicated, this form grows with
Yucca elata, baccata being absent; but it blooms a full
month earlier than the associated species. Its fruit, like
that of several of the other baccate species, is usually
long beaked, and the seeds are tunneled in the manner
characteristic of the work of Pronuba, the pulp being per-
forated by the escaped larvae. I was unable to study this
species in bloom, but large fruits gathered some three
weeks after fertilization show none of the constrictions or
indentations which so commonly mark the ovipositing punc-
tures of the Pronuba moths, which leads to a suspicion that
the eggs may be deposited in the upper part near the stigma.

Y. VALIDA, Brandegee. — In admitting this species to the
list of Yuccas published in the Third Report, I had over-
looked the fact that Mr. Brandegee* himself has referred

* Proc. Calif. Acad. (2), iii. 175.

FURTHER STUDIES OF YUCCAS. 193

it to baccata. The smooth leaves of the specimens I have
seen are, however, quite unlike the rough foliage of the
usual northern form of baccata, and the question of the dis-
tinctness of valida may still be kept open. I think it very
probable that it will be found in the heart of Mexico, where
several little-studied Yuccas of the baccata set occur, as
well as in its present range on the peninsula of Lower Cali-
fornia. Nothing is known of its pollination.

Y. FILIFERA, Chab. — Nothing is known of the pollina-
tion of this Mexican tree Yucca, except that herbarium
specimens of its fruit show the work of Pronuba larvae,
from which Professor Kiley infers that a large and interest-
ing species of moth peculiar to it will be discovered.*

B. CLISTOYUCCA, with leathery or spongy indehiscent fruits .

Y. BREVIFOLIA, Engelin. (PI. 6-9, 21)f . — This, our largest
tree Yucca, is interesting from several points of view.
Seedlings possess decidedly glaucous flexible leaves, rather
similar to those of young WJiipplei. At first a fleshy
round-pointed caudex develops below ground, from which
long simple tough roots spread in all directions ; but
this original descending axis disappears with age, so that
the old tree has a flat or irregular basal disk, from which
the tough roots, now as thick as a lead pencil, run into the
soil for a long distance. As a rule each plant forms only a
single trunk, but occasionally laterals develop, generally as
a result of injury to the main stem. Until it is eight or
ten feet high, the trunk is unbranched, and covered
throughout with the very rough and rigid, mostly yellowish-
green leaves, the lower of which are reflexed. When of
about this size, it blooms for the first time (PL 6), after

* I. c. 121; Proc. Biol. Soc. Washn., vii. 96; Insect Life, iv. 371. As
a further reference to this species should be given Fenzi: Boll. Soc.
Tosc. ortic. xiv. 1889, 278, with plate.

f See an article by Shinn, on "The Land of the Tree Yuccas," in
American Agriculturist, 1891, 689.

13

194

MISSOURI BOTANICAL GARDEN.

which two or three stout branches usually develop by the
side of the original apex, which now has ended its growth.
When these have reached a length of two or three feet
each forms a terminal inflorescence, and branches in its
turn, in this way giving rise to a repeated forking or
tripartition. On an overturned trunk, however, several of
the stronger branches usually become erect and grow to a
height equal to that of young trees, before blooming and
branching (PI. 8), but so far as I have seen they do this
without forming roots of their own, their supply of food
and moisture coming through the persistent roots of the
main trunk.* On the large stems, and even on some of the
larger branches of old trees, the reflexed leaves gradually
fall away, and expose to view a very thick gray bark, deeply
fissured into quadrangles measuring about 1X2 inches.
As the trunks increase in height they also become much
thicker, the loosely fibrous, water-soaked wood being marked
in concentric rings, resembling those of Dicotyledons and
Conifers, f At the base, these older trees dilate quite
abruptly, from the development of a circle of thick con-
fluent roots, which correspond to those so commonly seen in
the form of more or less marked prolongations of ridges
and buttresses on Dicotyledons, and constitute the root-
bearing disk mentioned above (PI. 9). These large roots
possess a structure superficially similar to that of the trunk.
When preparing to flower, this is one of the most
attractive of all the Yuccas, the ovoid inflorescence buds,
each as large as an ostrich egg, being closely invested by
large thick white bracts, after the manner of a banana
inflorescence ; but the bracts soon become dry and crum-
bling, and the expanded cluster, though of very compact

* An excellent wood cut showing this habit of growth occurs in the
Gray Herbarium, evidently clipped from one of the English horticultural
journals, but I have been unable to obtain a more exact reference to it.

t The structure and mode of thickening in arborescent Liliacese is very
iully treated by Roseler in Pringsheim's Jahrb. f. wiss. Bot. 1889, xx.
l>92-348, with several plates.

FURTHER STUDIES OF YUCCAS. 195

habit, is of an inconspicuous greenish white, and possesses
an odor which is so oppressive as to render the flowers
intolerable in a room, although the usual designation of
fetid is not strictly accurate.* Though the flowers differ
somewhat from the common Yucca form, they are quite as
variable as those of other species of the genus, and range
from globose to nearly oblong, or even prismatically pyri-
form when first opening. The petals differ from those of
other species in being very thick, sometimes measuring as
much as a quarter of an inch, and correspondingly rigid,
and on different plants they vary from glabrous to very
pubescent, and from glossy to quite dull, but usually with
the waxen appearance so commonly seen in the genus.

The filaments here are generally much shorter than the
pistil, against which they are very closely applied except
near the top, where they are often clavately thickened, and
the lower part is usually villous papillate. The pale lemon
yellow anthers differ strikingly from those of eastern spe-
cies, and in degree from those of other Calif ornian Yuccas,
in dehiscing only some forty-eight hours after the flower
has opened, while the stigma appears to be fully receptive
at the time of first expansion.

The whitish-green almost conical pistil is destitute of a
clearly marked style such as baccata and filamentosa show,
but its upper part is not occupied by the ovarian cells, and
so is virtually stylar. The lobing between the carpels at
top is so slight that the stigma is almost equally 6-notched.
The stylar canal is rather ample above, but its connection
with the ovarian chanibers is through a series of slits,
rather than open pores, and, at least after pollination, the
passages are often occluded by the conducting tissue. The
septal nectar glands are less developed in this species than
in any other which I have studied. They are always nar-
row, and in some cases do not reach below the upper third

* Cf. Parry, Amer. Naturalist, fc*. 141 ; abst. in Gardeners' Chronicle,
». s. iii. 492.

196 MISSOURI BOTANICAL GARDEN.

of the ovary. Externally they open in the usual manner ,
but the deep outer septal grooves are little if at all expanded
into a conducting channel, though they reach to the base
of the pistil in the usual manner and expand there into
triangular spaces. I have not observed any evidence that
the septal glands secrete at all, nor is the stigmatic secretion
as abundant here as in most species.

The dark colored Pronuba synthetica, which Professor
Kiley * describes as peculiar to this Yucca, rests during the
day within the flowers in much the position already de-
scribed for the eastern P. yuccasella, or, especially when
disturbed, retires between the densely crowded flowers,
where it is protected from most dangers ; but it is more
active through the day than its eastern congener. Towards
evening the moths become quite active, and it is probable
that copulation of the sexes occurs before night, for I have
not seen male moths at night within the flowers where the
females were occupied in oviposition. There is also reason
to believe that the latter accumulate their loads of pollen at
an early hour, though this again is only inference, since I
have not witnessed the operation, even in the cases in
which I have suspected that a moth was so employed, owing
to the peculiarly closed condition of the flowers. Unlike
the other known species, this Pronuba appears slow to take
flight. Though it is easily disturbed, so as to run about
and seek concealment between the flowers, I have seen it
take to the wing only a few times, and then it merely sailed
down to the ground, not far from the tree. This apparent
indisposition to leave the flowers may, perhaps, be con-
nected with the almost constant occurrence of high winds
on the desert. Whatever its cause, this habit of the moths
appears to. restrict cross-pollination to flowers of the same
plant more closely than is the case with other Yuccas,
though there must be frequent flights from plant to plant

* 1. c. 121, 141; Proc. Biol. Soc. Washington, vii. 94; Insect Life, iv.
370. (This was first called P. paradoxa, but without description.— Riley
Proc. Wash. Ent. Soc. 1888, i. 154, and Insect Life, i. 372.

FURTHER STUDIES OF YUCCAS. 197

in quiet weather, and especially at night, when the wind
sometimes falls; and the development of the stigma two
days in advance of the stamens of a given flower, renders
close fertilization in the strictest sense improbable.

The light yellow pollen is in such marked contrast with
the smoky tint of the moth, that laden females are recog-
nizable from a considerable distance, and notwith standing
the failure of direct observation, there is every reason to
believe that the latter collect their burden from the older
flowers with the same deliberateness that has been observed
in the other known species of Pronuba, since it is held
under the well developed tentacles in the same manner as
by them.

On first examining the flower clusters of brevifolia, I
was impressed by the remarkable symmetry of most of the
fertilized pistils, some of wThich had already reached half
the size of the mature fruit, which is in marked contrast
with the constriction or indentation of the eastern capsular
Yuccas at the point where the ovary has been punctured in
oviposition. This absence of deformity was explained,
however, when the act of oviposition was witnessed, for
the moth pierces, in this species, the uppermost part of the
style, conveying its eggs down to the ovary through the
stylar channel, — the course followed by the pollen tubes.

The female of most species of Pronuba seeks for a fresh
flower in which to deposit her eggs, showing preference for
one in the first night of expansion. To this she is probably
impelled by the impulse to insure for her offspring a suf-
ficient supply of food, the younger flowers being less likely
than the older to be already overstocked with eggs. This
instinct is particularly marked in P. synthetica, which I
have never seen ovipositing in any but the youngest flowers,
while I have repeatedly seen the pollen-laden moths force
themselves into the very narrow clefts between the rigid
sepals of an opening bud, their flattened form facilitating
this, after which only the most fragmentary glimpses of
their work were possible. But during something over a

198 MISSOURI BOTANICAL GARDEN.

week in the early part of April, spent at Hesperia, Cali-
fornia, where brevifolia is very abundant, I was fortunate
enough to observe many of the moths at work in somewhat
more open flowers, where their operations could be observed
in detail by the use of a bull's-eye lantern, to which they
show about the same tolerance as the other species.

When about to deposit an egg, having selected a suitable
flower, the female of synthetica runs to the bottom of the
stamens much as yuccasella does, makes a rapid more or
less complete circuit of their bases, and then quickly as-
cends to the very top of the pistil, her thorax rather
higher than the end of the stigma, and with her short but
strong ovipositor cuts through the thin wall, into the stylar
channel, rarely as much as 2 mm. below the tip of the
stigma, meantime holding fast to the pistil, the stamens
being below her reach. The long extensile oviduct is then
passed through the puncture, the egg being laid apparently
within the ovarian cell, along the funicular end of the
ovules. In removing the oviduct the moth not infrequently
carries her body across the stigma, so that at first sight she
appears to be withdrawing it directly from the mouth of
the stylar canal ; but I have never seen her make direct use
of this canal. The operation consumes more time than
does the oviposition of either yuccasella or maculata as I
have observed them, and usually takes altogether from two-
and-a-half to three minutes. Sometimes two or more eggs
are laid before the stigma is pollinated, but commonly after
laying each egg the moth retreats to the bottom of the
flower and then again ascends the pistil until her head is
brought even with the stigma, when she uncoils the large
tentacles from their resting-place against her load of pollen
and passes them back and forth in the stigmatic chamber,
with almost the same motion as the eastern species, usually
making use of one of the stigmatic notches. While so
employed she carries the rather short tongue almost straight
out above the stigma, but I have never seen her make any
use of it to force pollen into the latter, nor has she beea

FURTHER STUDIES OF YUCCAS. 199

observed to attempt to feed on the slight stigmatic secre-
tion nor to search for food at the base of the flower, where,
if anywhere, the nectar of the septal glands should be
found.

In this Yucca, the short spreading pedicels do not become
erect after the fertilization of the flowers, as is the case
in the capsular species, nor do they become markedly
pendent as in gloriosa and all of the baccate species, but
they maintain their original direction during the ripening
of the fruit. As in all of the Yuccas, the maturing fruit
develops a rather firm but thin core-like endocarp imme-
diately surrounding the seeds, but in this species the thick
exocarp, instead of becoming pulpy as in the baccate spe-
cies, or hard as in the dehiscent capsular section, assumes a
spongy texture. The ripe fruit, readily breaking from the
tree, consequently possesses large bulk and low specific
gravity.

Y. GLORIOSA, L. — Professor Kiley* states that this
species, which occurs in the aloifolia region of the south-
east, is pollinated by Pronuba yuccasella when it chances
to bloom in the season of the moth, which appears
when the earlier forms of Y.filamentosa are in flower; but
its blooming is more commonly later, often autumnal, so
that it less frequently produces fruit than aloifolia, and
Dr. Mellichamp writes me that although he has seen many
blooming plants he never has seen fruit of gloriosa but
once, and that was from a summer inflorescence. Like
aloifolia, the present species, in some of its rather numer-
ous forms, is said to fruit occasionally when Pronuba does
not occur to pollinate it.f Engelmann has shown, how-

* l. c. lie, 117.

t Ellacombe, in the Gardeners' Chronicle for 1880, xiii. p. 21, reports
that in England he has more than once had well formed fruit on T, re-
curvifolia, but the seeds did not come to maturity ; and in the same
journal for 1885, xxiv. p. 628, he mentions what appears to be the same
form, under the name of T. recurva, as having fruited in 1876, some of
the fruits and seeds having been sent to Kew and to Dr. Engelmann, a
few abortive fruits, which soon fell off, having also appeared in 1885. On

200 MISSOURI BOTANICAL GARDEN.

ever, that forms of aloifoHa have been cultivated frequently
under the name of gloriosa or wrongly referred to that
species,* and an editorial mention in the American Agri-
culturist for 1872, xxxi. p. 461, of the apparent absence
of insects from the pulpy fruits ' ' as soft as a banana ' '
of gloriosa, in Georgia, undoubtedly refers to aloifolia.
Professor Riley limits the power of self-fertilization so
far as known to aloifolia ;f and it may be questioned
whether the French gloriosa seedlings mentioned by him
in a quotation from The Garden^ were not really aloifolia,
though it is not distinctly stated that they were not the
result of artificial pollination. I have no personal knowl-
edge of the fruiting of true gloriosa except in the case
figured on plate 7 of the Third Garden Report, where a
specimen 'cultivated in Washington produced fruit side by
side with a. plant of aloifolia, and in this case the fruits
were more or less deformed, as if by Pronuba.

A rather narrow-leaved form of this species, cultivated
in the Garden under the name of Y. nivea, bloomed in
the early part of September, 1892, and showed nearly as
great activity of the septal glands as the specimen of
Guatemalensis already described, the nectar appearing in
considerable drops within the bottom of the perianth, about
the almost pilose bases of the filaments. While the aloifo-
lia of the Garden was fruitful without the aid of Pronuba
or hand pollination, and both aloifolia and Guatemalensis
yielded fruit when artificially pollinated, this plant set
no fruit, though a number of flowers were pollinated by
Mr. Webber. It will be of interest, therefore, to have
observations made on gloriosa, whether wild or cultivated
in its native region. The later blooming of this species,

the other hand in a popular account of Yucca pollination, in his Pflan-
zenleben, ii. 155, Kerner von Marilaun states that the fruit of this
species is quite unknown both on wild and cultivated plants, and it
is said that the moth adapted to gloriosa has become extinct.

* Trans. St. Louis Academy, iii. 211 ; Collected Writings, 297-8.

t Proc. Amer. Assoc. Adv. Sci. xxxi. 467.

I Proc. Amer. Ass. Adv. Sci. xxix. 624.

FURTHER STUDIES OF YUCCAS. 201

like that of certain forms of filamentosa, involving, as it
appears to do, a loss of the services of Pronuba and conse-
quent sterility in all but exceptional cases of early blooming,
is especially worthy of study, considering the usual close
correspondence of the period of blooming of the Yuccas
with that of the appearance in the perfect form of their
Pronubas.
c. CELENOYUCCA, with dry ', septicidally dehiscent capsules.

Y. RUPICOLA, Scheele. — No observations have been re-
corded on the pollination of this Texan species, which
Professor Eiley* believes may have a distinct Pronuba. It
is not uncommon from Fort Worth southward, on the
black soil with intermingled limestone, but I failed to study
wild plants. At Dallas, however, through the kindness of
Mr. J. Reverchon, I was able to examine specimens culti-
vated on his place, which were blooming simultaneously
with the wild Y. glauca, var. stricta and frequented
by Pronuba yuccasella like the latter. These plants are
abundantly fertile (each crown dying after blooming), and
the structure of the flower indicates that the moth works
on them as she does on the filamentosa group, though I
was unable to observe her actions. Their seedlings are
now spontaneous about the place, and so variable that Mr.
Reverchon suspects hybridization with the native variety of
glauca, as well as cultivated forms of filamentosa. This
will prove an interesting subject for future study, since the
habits of Pronuba in caring for her young are so highly
specialized, and the details are so minutely carried out, that
it was hardly to be expected that a given individual would
indiscriminately pass from one species of Yucca to another,
though on the other hand, it is known that the more eastern
species are all pollinated by representatives of the single
species of Pronuba.

Y. ELATA, Engelm. (PL 10, 15, 22).— Beginning in west-
ern Texas, about the limits of glauca, this Yucca gradually

* L c. 122.

202 MISSOURI BOTANICAL GARDEN.

increases in size as one passes into Arizona, where it
becomes a rather large tree, but of far simpler habit than
brevifotta, and much smaller than the larger plants of that
species. Its underground axis is of the glauca type, —
long, tough and branched,* — so that it is difficult to remove
even the very small plants from the ground. The inflo-
rescence appears to be terminal, so that the crown which
has bloomed has its apical growth destroyed ; but a lateral
bud develops into a new crown, and in time a number of
thick new heads may form in this manner, making a pluri-
capitate plant. The shortness of these branches, and their
dense covering of long spreading leaves, contrasted with
the frequent slendernesss of the trunk, after its lower leaves
have become reflexed and dry, gives the tree a peculiar and
not ungraceful appearance, quite different from that of
any other species native of the United States. The old
flower stalks, when above the reach of cattle, usually hold
their dehiscent capsules for at least a year, and at length
break away without disarticulation above the base, which
persists for years along the side of the stem, closely applied
to it because of the erect sympodial habit of the latter.

At Eagle Flat, Texas, I was able to spend several even-
ings about the first of June in studying the pollination of
this species, which there rarely becomes six feet high and
begins to bloom when not more than two feet high, so that
observations are more readily made than on the taller
plants of southern Arizona.

The flowers are nearly pure white, with quite acute thin
petals, and conform in most respects to those of glauca.
The style, however, is white, as in nipicola and filamen-
losa, and its segments are little thickened dorsally. The
septal nectar glands are very well developed, as in all of
this group, and reach to the base of the ovary. They ap-
pear to be slightly more active than in related species, for
a little nectar was recognized in several flowers, and two

Engelmann, Coll. Writings, 279, 280.

FURTHER STUDIES OF YUCCAS. 203

species of small bees* were taken, probing the outlets of
the conducting grooves at the base of the pistil ; but these
insects were not seen to visit the stigma, so that they
play no part in pollination. Considerable numbers of a
moth, which Professor Kiley determines for me as Acontia
Arizona, Hy. Edw., were seen resting in the flowers during
the day, and settled about them, especially on the pedicels
near the base of the perianth, at night, but I was not
fortunate enough to determine the occasion of their visits
to the plant, though I suspected that their larvae might
develop on it. So far as can be seen, they play absolutely
no part in its pollination, though it may be that they feed to
a greater or less extent on the nectar. The stamens shed
their pollen promptly on the opening of the flowers, and
this is devoured by various small flies with the same avidity
as in glauca, and with about the same prospect of effecting
occasional casual pollination as in that species. t

Like the eastern Yuccas, elata is pollinated by Pronuba
yuccasella, the work of which was repeatedly observed in.
detail at Eagle Flat, where the moths were abundant.
During the day, like the Eastern moths and those of baccata,
they rest in the flowers with their heads directed to the base
of the petals. Shortly before sunset many of them be-
come active (as is the case on filameniosa at St. Louis),
the females beginning their work of oviposition and pol-
lination, while the males run and fly actively from flower
to flower in search of their mates ; and this is continued
through the greater part of the night.

When about to deposit an egg, the moth here, as on
jilamentosa, runs nervously about within the bottom of the
flower, then scrambles to the top of the pistil and backs
down between two stamens by a succession of jerks until
her head is about level with the base of the style. Hold-
ing to the pistil by the pro- and meso-thoracic legs, the last

* Determined by Mr. Charles Robertson as Agapostemon Texanus,
and Halictus albipennis, 9 .
f See a note by the writer in Riley, i. c. 126.

204 MISSOURI BOTANICAL GARDEN.

pair not infrequently carried out over the filaments, she
then punctures the ovary and the egg is consigned to its
place in the manner so well described by Riley for fila-
mentosa ; but as a rule the operation appears to consume
rather less time on data than on the other Yuccas I have
studied. Usually each oviposition is followed by pollination,
in which, so far as I can see, the moth acts precisely as on
filamentosa ; but in a few cases two eggs were laid before
pollen was carried to the stigma, and under the bright light
of the lantern the actions of the moth are sometimes so
disturbed that she will leave a flower after ovipositing, with-
out subsequently pollinating it. I have also observed on
this species that she sometimes interrupts the act of polli-
nation to coil the tentacles against her load of pollen, after
which they are again inserted in the stigma, thus securing
for the latter a larger amount of pollen ; but I have no
doubt this procedure is as common on the other species pol-
linated by yuccasdla. In one instance, a moth disturbed
by the light while ovipositing left the flower without polli-
nating it, but her first act on going into another flower was
to thrust her pollen-laden tentacles into the stigma, though
it appears to be unusual for this to precede oviposition.

The collection of pollen from the anthers was not closely
observed on elata, but on several occasions the moth, when
disturbed in oviposition, ran upon a stamen, shaking it quite
violently and making several passes at the anther with her
tentacles, as if impelled by fright to discontinue one of her
customary occupations only to engage in another, — though
her motions were too quick and nervous for me to see that
she actually gathered any pollen. There is, however, no
reason to doubt that the collection of pollen is similar to
that on Jilamentosa, where, however, it is by no means
always slow and easy of detailed observation.

When I passed over the Texas and Pacific road again,
about a month later, a fair crop of partly grown fruits was
seen, the usual constriction or indentation being noticeable
over the Pronuba punctures. At Benson, in southern

FURTHER STUDIES OF YUCCAS. 205

Arizona, where elata assumes much larger proportions,
though it bloomed very freely this year, I did not suc-
ceed in finding any of the moths in a day-light search in
the early part of June, just as the species was coming into
bloom, nor were many ripening capsules to be found when
I again visited this locality toward the end of the month.
But the few fruits which had set showed the usual Pro-
nuba deformity, and a considerable number of last year's
capsules were found, all containing the remains of tunneled
seeds, and perforated by the escaped larvae.

Y. GLAUCA, Fraser, Cat. 1813, not Sims. ( Y. angusti-
folia, Pursh, 1814, and most recent writers).* — It has long
been known that the pollinator of this representative Rocky
Mountain species is JPronuba yuccasella, which appears
coetaneously with its flowers in the west and southwest,
but, being more closely connected in the east with the later-
blooming filamentosa, only exceptionally appears early
enough to pollinate even the latest blooming flowers of
glauca on plants cultivated in Washington and St. Louis f
(where a few capsules were again matured in the sum-
mer of 1891). The only observations on the behavior of
the moth on wild plants that I know of are those reported
by the writer in 1891 from the vicinity of Manitou, Col.|
Incomplete as these are, they show that her actions are
quite the same as on filamentosa.$

* Though for reasons of expediency it would be better to preserve for
this plant the name of angustifolia, under which it is universally known,
the short description in Eraser's Catalogue is sufficiently characteristic, in
connection with the northern locality from which his specimens were
obtained, to make it necessary to restore his name. The later Y. glauca,
Sims, is an entire-leaved plant which I should refer to jilamentosa.

t Riley, I. c. 116, 121, 128. J See Riley, L c. 124.

§ The principal references under this species are as follows : Bruner,
Entomol. Bull. U. S. Dept. Agriculture, ii. 9. Meehan, Bull. Tor-
rey Bot. Club, iv. 63; Proc. Phila. Acad. 1873, 414; Proc. Ainer. Ass.
Adv. Sci. xxx. 205; Amer. Nat. 1881, 807; Proc. Phila. Acad. 1888, 275,
general abstracts in Proc. Amer. Ass. xxxvii. 284 and Bot. Gaz. 1888,
237. Eiley, Trans. St. Louis Acad. iii. 570; Mo. Ent. Kept. v. 159; Insect
Life, i. 363 ; Kept. Mo. Bot. Gard. iii. various places.

206 MISSOURI BOTANICAL GARDEN.

The typical Yucca glauca, as represented in Colorado
and Kansas, spreads below ground by a series of rather
slender but very strong axes, and in its more highly
developed form has a more or less developed mostly pros-
trate stoutish trunk above ground. So far as I know,
whether caulescent or acaulescent, a given axis usually
blooms repeatedly.

Y. GLAUCA, var. STRICTA, (Sims.). (Y. angustifolia,
var. mollis, Engelm.) (PI. 22). — In its broader flaccid
leaves, occasionally an inch wide, this forms an approach
from glauca to the Eastern filamentosa, but its range, —
Arkansas, Louisiana and Texas, — brings it strictly within
the region of the former and its immediate allies. Unlike
the more representative glauca, however, a given crown
seems more likely to fruit but once, though the subterran-
ean parts are similar in both. Its delicate greenish-white
flowers, most commonly in a simple raceme, possess the
general characters of those of the type, and are slightly
fragrant. The styles, though somewhat variable in color,
are commonly bright green as in the type, so that they
contrast with the ovary, which is colored similarly to the
perianth. The stylar canal is open and in evident com-
munication with, the cells of the ovary, and at times con-
tains a plentiful secretion. No nectar was observed at
Dallas, Texas, where I had an opportunity of examining
the flowers in several localities, but the septal glands are
large and with large conducting grooves, as is generally the
case in the filamentosa group.

Many years ago Boll * made a number of observations
about Dallas on the Yuccas, some of which were doubtless
of this variety. While he did not at first discriminate be-
tween Pronuba and the related Prodoxus decipiens, — which
Professor Riley has well called the Bogus Yucca Moth, —
and especially the still more deceiving Prodoxus intermedium,

* Boll, Stettin. Entomolog. Zeitung, 1876, 401, quoted by Riley i»
Trans. St. Louis Academy, iii. 571.

FURTHER STUDIES OF YUCCAS. £07

and fell into some other serious errors, he appears to have
been the first to observe the collection of pollen by the
female Pronuba, though not with the detail given by Pro-
fessor Eiley in the account of his own observation of this
operation on Y . Jilamentosa .*

The pollinator of this variety, as of the more representa-
tive form of the species, is the white Pronuba yuccasella.
As on other Yuccas, the moth is quite sluggish within the
flowers during the day, apparently considering itself con-
cealed by its protective coloration. Numerous laden females
were taken and observed about the flowers at night, and copu-
lation within the flower was several times seen in the evening,
but I was unfortunately not able to see these moths engaged
in either pollination or oviposition. The pale poll en, how-
ever, is very evident in the green stigmas, where there is lit-
tle reason to doubt they have placed it. Egg punctures were
also observed in numbers, in such a situation on the ovary as
to show that the moth occupies the same position when ovi-
positing as on filamentosa. On the older panicles a fair
percentage of fruit was maturing at the time of my exam-
ination at Dallas, and showed the usual Pronuba constric-
tions, and several capsules of the preceding year which were
found had been perforated by escaping larvae, and contained
remnants of tunneled seeds.

At Putnam, Texas, considerably west of Dallas, a larger
form of what I take to be this variety of glauca occurs,
with narrower leaves ; and about the end of May this was
passing out of bloom, just as elata, still further west, was
beginning to flower. At this place, fewer capsules had
set than about Dallas, but these showed the irregularities
indicative of oviposition by Pronuba, which had quite dis-
appeared ; and some of the stalks of the preceding year
still bore capsules which were marked by the escape
perforations of her larvae.

* Proc. Amer. Assoc. Adv. Science, 1882, xxxL 467-8; Third Garde*
Report, 106, pi. 38, f. 2.

Private library of
J. ELIOT COIT
Please return.

208 MISSOURI BOTANICAL GARDEN.

Y. FILAMENTOSA, L. (PL 11, 22). — This species is the
subject of nearly all of the pollination observations hereto-
fore published, and its interrelations with Pronuba yucca-
sella are so well known that I need scarcely do more than
refer to Professor Riley's account in the last Garden Re-
port. In St. Louis the observations of preceding years *
have been repeated by myself and others, and on several
occasions the collection of pollen was again witnessed, but
in the same imperfect manner as last year, owing to the
haste of the moth. Although special attention has been
given to this point I have failed to see the moth attempt
to feed on either the stigmatic secretion or the septal
nectar, nor have I been able to reconvince myself that she
makes use of the tongue in pollination, as I once thought.
As in the case of Yucca elala, the moth, when disturbed
by the lantern while ovipositing, sometimes attacks the
stamens, as if intending to reinforce her load of pollen, but
in most cases without proceeding far in this before retreat-
ing to the resting position within the base of the flower, or
leaving the latter. In addition to the insects heretofore
seen in the flowers of this species, I have this year seen
several specimens of a rather large flower beetle, Trichius
piger, in the bottom of the flowers, with their heads at the
outlet of the nectar grooves as if feeding on the small
amount of secretion.

HESPEROYUCCA.

Filaments aduate to the petals below : po lien agglutinated in coherent
masses: style slender: stigma capitate, hyaline-papillate, with a micro-
scopic axile canal: fruit capsular, loculicidal.

Y. WHIPPLEI, (Torr.) Baker. (PI. 16, 23).— From the
San Bernardino Mountains north to the latitude of
Monterey and south into Lower California in the Coast
Range, this peculiar species is very abundant, especially

* See Eiley, 1. c. 123 etc. Ellacombe in the Gardeners' Chronicle
for 1872, p. 1457, Morse, ibid. 1885, xxiv. 598, and Smith, ibid. 1872, 1391,
report spontaneous capsules on this species in England. This should be
compared with the references given under gloriosa.

FUKTHER STUDIES OF YUCCAS. 209

through the Tehachapi region, the lower mountains being
often densely covered with its large frequently cylindrical
panicles or old fruit stalks. The most typical form, as it oc-
curs in the Cajon, Tehachapi, and San Luis Obispo regions, is
almost always cespitosc, sometimes with eight or ten crowns
clustered over a single root, owing to the formation of
lateral branches near the base of the main stem, even while
this is quite young. After blooming, a given crown dies,
but the several heads of these cespitose plants may pro-
long the life of the plant through a series of years, until
the last of them has flowered. The leaves of this f orni are
commonly, though not always, quite rigid.

The flowers are as variable as in the true Yuccas, ranging
from globose to bell-shaped, and there are great individual
differences in the degree to which they expand, but they
are not typically rotate, as Dr. Engelmann was led to
believe by some photographs looking directly into rather
widely opened flowers. They differ from those of other
species in having the glabrous (but still minutely granu-
lated) filaments attached to the lower part of the petals, —
a character not well shown in the figures in the last Report,
so that as they open the stamens are drawn away from the
ovary instead of lying in close apposition to it. The small
oval anther cells are commonly tipped by a bunch of white
hairs, though in specimens observed on the mountain sides
above San Luis Obispo these were reduced to one or two
on each cell or were apparently entirely wanting, and I have
no idea as to their function. On dehiscing, the cells con-
tract in such a manner as to expose the pollen freely, but
at the same time prevent it in most instances from falling
out, as it so frequently does in the true Yuccas. As Riley
has already shown,* the pollen of this plant is not loose
and powdery, as in Yucca proper, but glutinous. The con-
tents of each anther cell, in fact, form a rather consistent
two-lobed moist mass, which is held by its lower part but
protrudes prominently from the open anther.

2j Q MISSOURI BOTANICAL GARDEN.

The pistil differs materially from that of the true Yuccas
in having the ovary free from those longitudinal depres-
sions which usually correspond with the appressed stamens,
and in possessing a short contracted style surmounted by a
capitate stigma, green toward the center, where it appears
slightly indented, and covered with very long hyaline deli-
cate papillae which are always moist with abundant secre-
tion that at length becomes almost gelatinous over the
middle of the stigma. From the central depression of
the stigma, a fine but unobstructed canal passes down
the style and communicates with the top of the cells
of the ovary. The nectar apparatus is well developed, the
septal glands, though narrow, commonly reaching to the
base of the ovary, while the conducting groove is of cor-
responding size. My observations lead to the conclusion
that the glands, though smaller than in the filamentosa
group, are more active than in other species studied by me,
with the possible exception of gloriosa and GuatemaleTisis,
for I have repeatedly 'seen considerable drops of nectar at the
basal outlets of the grooves, especially in the early morn-
ing or in damp foggy weather when evaporation was slow,
and in pendent flowers similar drops have been seen several
times over the grooves at either the middle or top of the
ovary, along the smooth surface of which they had appar-
ently rolled from the outlets of the conducting grooves.

Professor Riley has shown that Whipplei is pollinated
by a distinct Pronuba, which he names P. maculata, of a
white general color, but somewhat variously mottled with
black, especially towards the ends of the wings.* He
records the occurrence of the moth in the vicinity of San
Diego, Los Angeles, Newhall, and Caliente. I have also
taken specimens at Summit in the Cajon Pass, at Saugus,
San Luis Obispo, and along the Santa Ynez river above
Santa Barbara, besides seeing evidence of its work in the

* I. c. 121, 139; Insect Life, iv. 370, note. For other notes by the
same author, see Proc. Ent. Soc. Washington, 1888, i, 154, and Insect
Life, i. 372.

FURTHER STUDIES OF YUCCAS. 211

old fruits both at Newhall and Caliente. The only other
insects observed by me in the flowers, were small flies and
beetles similar to those so frequently seen in the flowers of
the Yuccas, a few small bees, and on one occasion, hive
bees. The latter were primarily attracted by an abundant
watery fluid on the outside of the flowers, of undiscovered
origin,* and entered the flowers only incidentally. The
others gathered nectar from the base of the corolla, where
the nectar grooves open. Neither were seen to touch either
the anthers or stigma, and it is doubtful if they carry pollen
from one to the other, even by accident, which is the only
way in which this could happen.

From its pronounced fragrance, which while it is of the
general yucca type somewhat recalls that of the tuberose,
its active nectar glands, pollen aggregated into crude
pollinia, and large capitate stigma covered with long moist
papillae, Whipplei would appear quite likely to be pol-
linated by visitors other than Pronuba ; and, as Professor
Riley has well said, of all the Yuccas it would seem to be
most easily self-fertilizable. In fact, in the lower part of
the Cajon Pass when the species was in the best of its
blooming period, very few Pronubas were seen ; and, while
there was a corresponding scarcity of setting fruit, a few
plants were found with more or less abundant, partly
developed but unusually diminutive capsules in which no
oviposition scars could be detected, and some of the fruit
of the preceding year was of the same dwarf character and
without either escape holes or the masses of tunneled seeds
almost invariably seen in old capsules elsewhere. Frequent
observation has shown that the pollinia may be deposited
on the margin of the stigma directly from the anthers in
closing flowers, particularly the small ones to which these
dwarf capsules correspond ; and it was, therefore, with no
little surprise that I noted, in contrast with this apparent
power of self-fertilization, that with this single exception, no

* See note under baccata for the occurrence of a similar exudation i»
species of Yucca proper.

212

MISSOURI BOTANICAL GAHDEX.

fruit whatever was found except that which clearly showed
the work of Pronuba. At best, therefore, I should say that
where its proper Pronuba is absent, WJilpplei has only the
limited power of self-pollination, or pollination by other
agents, that is possessed by aloifolia among the true Yuc-
cas. I have also no evidence that pollen tubes ever develop
in such a manner as to reach and fertilize the ovules
from pollinia placed on the margin of the stigma, although
search was made for something of the sort; and a deter-
mination of the extent to which fertilization in this manner
is possible must be made by a series of experiments such as
I could not carry out in the time at my disposal.*

The characters of Pronuba maculata, have been so fully
given by Eiley that nothing need be added to his descrip-
tion. From the frequently open character of the flowers,
and, especially, the withdrawal of the stamens from the
pistil, these moths are, however, constrained to behave
quite differently from the other species of their genus ; and
very probably in connection with the more diurnal nature
of the Hesperoyucca flowers, they are far more active in
the day time than their congeners are. Unless locally ab-
sent, they are readily observed whenever the flowers are
examined, either resting in them or engaged in pollination
or oviposition, and at first sight it is difficult to say whether
they are quiescent or engaged in the latter operation, for,
unlike the other known Pronubas, they rest with the head
toward the stigma, usually standing upon the side of the
ovary, — a position almost identical with that taken in ovi-

* Since the above was written, Professor Riley, under date of October
13, 1892, writes me that in a manuscript report on the pollination of
Whipplet, Mr. Coquillet of Los Angeles records the seeding this year of a
number of pods or panicles which he had covered with gauze before any of
the flowers opened. Professor Kerner von Marilaun (Pflanzenleben, ii.
155, figures 1 to 5), states that in repeated cases of blooming in the
Vienna Garden this species has never matured its fruit. The figures
which accompany his account of Yucca pollination represent some Eu-
yucca, — apparently a form of jilamentosa, — though they bear the name
WMpplei; and the moth represented as pollinating the flower (adapted by
the artist from Riley's figures), is yuccasella.

FURTHER STUDIES OF YUCCAS. 213

positing. While in this attitude they are very observant,
and the approach of one's face, even at a distance, causes
them to retire further down the pistil. When so disturbed
they are also very apt to drop suddenly from the flower and
take wing, seeking a new retreat.

I have not seen the collection of pollen by the typical
form of this moth, but, from the way in which the load is
carried, there is no doubt that it is accumulated in the
manner presently to be described for the pollinator of what
I take to be the Yucca graminifolia of Wood, and I see
no reason to doubt that it frequently takes place in the
bright daylight, as both oviposition and pollination do.
Either of the latter operations may be witnessed at any
time during the day, if the flowers are not approached
too suddenly.

When the moth is about to deposit an egg, she usually
moves about in the lower part of the flower much as the
other species do, commonly dragging the tip of the ovi-
positor along the parts she walks on as if wiping off
extruded secretion, but also seemingly using it as a tactile
organ while she assumes the position best suited to ovi-
position, which is nearly the same as that taken while at
rest. Standing on the side of the pistil, she then bends the
abdomen sharply forward so as to bring the ovipositor
to about the middle of the ovary, which she pierces at
the thinnest part, namely, about 1 mm. from the septal
groove. As a general thing not more than six eggs are
laid in a given pistil, — one on either side of each septum, —
and frequently the number is smaller than this, so that
even if they all hatch, which is not likely to be the case,
there is rarely more than one larva to each tier of seeds,
and consequently a fair percentage of the seeds are allowed
to come to maturity . In the very succulent white ovary
the puncture made in laying an egg is usually seen easily
immediately after the ovipositor is withdrawn, and a rather
large drop of clear sap not infrequently exudes from it
within a short time.

214 MISSOURI BOTANICAL GARDEN.

Having withdrawn the oviduct, in doing which she moves
up so that her head is about level with the stigma, or even
before this organ is entirely freed, the moth usually pro-
ceeds to pollination ; but it is not infrequent for two eggs
to be laid between each two visits to the stigma, and, owing
to her peculiar alertness, she appears to be even more easily
frightened into omitting pollination than are the other
species of Pronuba. Standing with her head at about the
height of the stigma, with the short tongue projecting out
in front, she uncoils her long tentacles from the compact
mass of pollinia, — which she carries similarly to the
other Pronubas, — only that small part of her burden which
adheres to the bases of the tentacles being removed from it,
and, raising her body on tiptoe, she very slowly saws the
tentacles back and forth across the top of the stigma, gen-
erally following one of the three shallow grooves, and very
carefully working their slender tips into the more or less
gummy exudation over the central depression. Sometimes
the operation is interrupted long enough to admit of the
tentacles being coiled back against the load of pollen and
again extended ; but the curious manner in which her head
is held back from the stigma as a rule prevents any of the
main load from reaching even the marginal papillae.

On first witnessing this operation, I was impressed by
the much slower motion of the moth than usual, and the
evident care which she took to run the ends of the tentacles
into the central depression of the stigma, which I then sup-
posed to be solid ; the subsequent discovery of the stylar
canal, communicating with the ovarian cells, showed that
it is into this narrow passage that she so carefully guides
the tips of her tentacles with their modicum of pollen, and
no doubt the abundant stigmatic secretion serves not only
to foster the development of the nascent pollen tubes after
pollination, but, wetting the tentacles, aids in the disinte-
gration of her mass of pollinia. These, if really related to
her work, would seem to have acquired their coherent
structure as a means of facilitating their collection, rather

FURTHER STUDIES OF YUCCAS. 215

than as an adaptation to their removal bodily from the
anther to the stigma as is the case in orchids and asclepiads,
where, however, special means of secure attachment to the
insect accompany this aggregation of the pollen grains into
a large mass.

As in the other capsular Yuccas, the pedicel of the fer-
tilized flower soon becomes erect, and the ovary shortly
begins to enlarge and assumes a bright green color. Owing
to the injury inflicted in piercing its wall, the part immedi-
ately about the puncture does not take a very active part
in this growth, and a cross section here shows a decided
difference in size between the punctured and unpunctured
half cells of the ovary, and, as the enlargement of the
capsule continues, a decided pit appears, mostly of a darker
green than the surrounding parts.

H. WHIPPLEI, var. GRAMINIFOLIA, (Wood). (PI. 13, 23). —
What I take to be this form, is the common Spanish Bayo-
net of San Bernardino, beginning near the foot-hills north
of the city and extending up the smaller canons and upon
the mountain sides to an elevation of 1000 feet or more,
and, in the Cajon Pass, reaching up toward Cajon Station,
where the steep ascent of the pass begins. Recent notes
from Dr. Yates, of Santa Barbara, show that a plant of
the general character of this variety occurs in the mount-
ains above that city, in addition to the typical Whipplei;
and it appears to pass eastwards from the San Bernardino
region, though I am not in possession of detailed informa-
tion as to its distribution outside of the limited area between
San Bernardino and the foot-hills north of that city. The
plants are very abundant around the Arrowhead Springs,
where the type of Whipplei does not occur, and I was
able to make a rather careful study of them there shortly
after the middle of April, when they were just coming into
bloom, as well as a month later, when their flowering period
was nearly past; and, still later, in company with Mr. S.
B. Parish, I had an opportunity to drive over the principal
part of the valley covered by this form, at a time when its

216

MISSOURI BOTANICAL GARDEN.

pollinator had almost completely disappeared, though some
spikes were yet blooming.

In aspect, this variety differs from the typical Whipplei of
the mountains in not being cespitose, and in its thinner,quite
flexible, often broader and longer leaves. Its flowers are
similar to those of the type except that they are commonly
more or less brown-purple, and they are as variable in
form. All about Arrowhead, at the time of my first visit,
there were evidences of the work of a Fronuba in last
year's capsules, which were very abundant, and I conse-
quently expected to be able to study the work of P. macu-
lata in the opening panicles. I was, however, surprised to
see that the only Pronuba found on the plants of this
vicinity, though possessing the usual maculata structure,
was of a beautiful jet black color, and, with the exception
of a single specimen, in which the thorax was dingy white,
this proved to be the case with the thousands of moths
seen or captured about Arrowhead and in the valley to a
point near Irvington. I have called this rnelanic form P.
maculata, var. aterrima.*

The females of this black Pronuba rest upon the ovary
with their heads toward the stigma, precisely like the typi-
cal maculata, while the males also commonly stand upon
the petals. Like the maculate moths, they are very alert,
and quite ready to drop from the flower and take wing
when disturbed. They are also active during the day, the
males, especially, running and flying from flower to flower
in quest of their mates ; and copulation is seen within the
flowers at all times of the day.

The collection of pollen was witnessed several times,

* Pronuba maculata, var. aterrima, n. var. Characters of the species, but
the chitinized parts smoky brown, and the scales of a dead black color
throughout, or a few pale ones near the tips of the primaries.— Living as
a larva in the forming seeds of Hesperoyucca Whipplei, var. graminifolia,
the flowers of which are pollinated by the female imago. In the foot-
hills immediately north of San Bernardino, California, April, 189:!.
Types deposited in the Entomological collections of the National Museum,
the Agassiz Museum and the California Academy.

FURTHER STUDIES OF YUCCAS. 217

under a cloudless sky, the first time nt about noon. Flying
into a flower, the rnoth runs about the bases of the stamens
after the manner of other species, then quickly clambers
upon the inner side of a filament, and, with the tentacles
extended over the pollinia, drags first one and then the other
out of the anther cells, pressing them together under the
throat, and subsequently compacting the mass together
much as yuccasella does the powdery pollen of other
Yuccas, so that the ball finally consists of as many as ten
or a dozen pollinia. So quick and energetic are the motions
by which the pollinia are removed, that the stamens are
often shaken quite violently, as I have before noted in the
more nervous attempts of yuccasella. Oviposition and
pollination, which were repeatedly witnessed, are performed
exactly as by the maculate moth, the very slow movement
in the latter operation being quite as striking.

The relationship of the Yuccas to one another and to
their pollinators, the Pronuba moths, would be far more
intelligible if we could trace their history back even a short
distance into the later geological time, because as Yuccas
and Pronubas both are undoubtedly of recent origin ; but
as was pointed out in the Third Report of the Garden, this
is as yet impossible, since no certainly identifiable Yuccas
exist in even the latest deposits, though plants bearing
more or less resemblance to them occur far back in the
geological epoch. In his paper so frequently referred to in
the foregoing pages, Professor Eiley has called attention
to the ancient type of vegetation represented by the tree
Yuccas. This is particularly true of Y. brevifolia, which
in aspect resembles restorations of the Carboniferous
Lepidodendron more nearly than any other form of recent
or fossil tree with which I am acquainted. The other
arboreous Yuccas are more like the Dracaenas in habit, but
the latter also belong to an antiquated type.

Though no single species extends across the continent,

215 MISSOURI BOTANICAL GARDEN.

the Yuccas occur in practically unbroken continuity from the
Atlantic coast in the vicinity of Fortress Monroe to Florida,
and across the Southwest and Mexico to California in the
neigborhood of Monterey, Y. glauca reaching well up on
the upper Missouri River, and Y. baccata following the
Rocky Mountains northwards into southern Colorado.
From this it may be inferred that they have become
specifically differentiated at a comparatively recent date,
an inference which is supported by the fact that notwith-
standing various dissemination contrivances which may be
held to be of still later acquisition, all of the species
except the distinctively West Coast brevifolia and Whipplei
may be broadly classed under the same type. The occur-
rence of so many species of the same floral type, and of
what may be called modern habit of growth, over a
common geographical area in the southern part of the
continent, while the apparently ancient brevifolia is
restricted to the desert region in or adjacent to California,
and the seemingly more highly differentiated Hespero-
yuccas occur only in the mountains near the latter region,
though each has its specific Pronuba quite different from
the one associated with the Eastern Yuccas, would lead one
to surmise that the geological record, if it had been pre-
served, would show that the first of the Yuccas were of
wide distribution, probably extending across the continent
on the higher parallels while the northern climate was less
rigorous than it now is, but receding to the south under the
advancing glacial cold. Indeed it seems reasonable to
suppose that the ancient type as represented in brevifolia.,
with an equally ancient type of Pronuba, has persisted in
the Pacific region throughout, perhaps owing to the series
of circumstances which have led to the preservation of the
Sequoias in the same region,* while the more widely
distributed species became differentiated and, with their
pollinator, passed to the south under new conditions.

* See Gray, Presidential Address, Dubuque meeting American Asso-
ciation for the Advancement of Science, — Proceedings, xxi. 1.

FURTHER STUDIES OF YUCCAS. 219

All of the Yuccas agree in the possession of a general
liliaceous type of flower, and in having compound pistils
with a stylar canal and septal nectar glands. The latter
characters, however, pertain to a considerable group of
Monocotyledons, and evidently antedate the evolution of the
Liliacese as an order.* If my view is correct, each of these
characters came to Yucca in a fairly advanced state of
development, from an earlier type of monocotyledonous
plants. In brevi folia or its immediate ancestors, as well
as in the eastern Yuccas, the stylar canal appears to have
been extended and amplified at top through the marginal
union of erect stigmatic lobes, so as to form the peculiar
stigmatic chamber into which the pollen must be thrust
in order to properly develop its tubes and fertilize the
ovules.

Originally having spreading stigmas, we may assume that
the progenitors of the Yuccas were slightly specialized ento-
mophilous flowers, pollinated by hymenoptera, diptera or
lepidoptera, which were attracted by the secretion of the
septal nectar glands. With the consolidation of the stigmas,
however, insects visiting the flowers for this nectar became
ineflicient pollinators, as may be seen when such insects
enter the flowers . of the existing Yuccas for the little
nectar still produced ; hence, with an economic reduction
of the secretion of these glands, may have come an addi-
tion of their function to that normally borne by the stigma,
in an increase in its secretion, so that the visitors, laden
with pollen unconsciously accumulated while in the flower,
should further visit the stigma on which some of their
burden might be rubbed while they were feeding. Dur-
ing this stage of its evolution the plant appears to have
proved especially attractive to some small moth, perhaps

* For a stylar canal in Agave see Danielli, Studi sull' Agave Ameri-
cana, Florence, 1885, 59, pi. 10 ; George and Wittmack, Gartenflora, 1892,
278, f . 55, but incomplete. References to the principal papers on septal
nectar glands are given in a short note by myself in the Bulletin of the
Torrey Botanieal Club, 1886, 135.

22Q MISSOURI BOTANICAL GARDEN.

fond of nectar, and with phytophagous larvae, which is to
be regarded as the progenitor of the Pronubas and their
close relatives of the genus Prodoxus, the history of which
has been so well summarized by Professor Eiley in the
Third Garden Report. Whether the first Prodoxids were
also pollen feeders, so that their mouth parts became
accidentally laden with pollen between their visits to the
stigma in search of its secretion, I cannot surmise. As my
friend Dr. Lind has suggested, they may have learned to
collect this substance and deposit it in the stigma through an
instinct such as prompts the mud-dauber to place its prey
about the point where its eggs are laid, or the bee to deposit
honey and pollen where it can be used by the lame, as
though its young were to be directly nourished by the pol-
len. At present, however, the act appears to be strictly
voluntary, without food compensation, and entirely con-
nected with the fertilization of the ovules. The fact that
the septal glands of the several species still secrete at least
a small amount of nectar may, as Riley believes to be the
case,* depend upon the indirect utility of this secretion near
the base of the flower in drawing insects other than Pronuba
away from the stigma ; or, as I am inclined to think, it may
merely indicate that the abortion of the glands is not yet
complete. The glands themselves need not be expected to
disappear or to be reduced in size to an extent correspond-
ing with their loss of activity under this latter supposition,
for their persistence does not itself imply any drain on the
forces of the plant, since they represent mere clefts in the
connate walls of the carpels which have united to make the
compound Yucca ovary. It is possible, however, that the
rather abundant stigmatic secretion is not, as I have sup-
posed, now being reduced from a still more abundant
quantity that once served as true nectar, — and this
assumption of a former nectariferous function of the stigma
would be superfluous if Dr. Lind's theory were correct, —

* i.e. no

FURTHER STUDIES OF YUCCAS. 2?1

since the Agaves, with an entirely different sort of pollina-
tion, possess an equally copious stigmatic secretion.

The Hesperoyuccas, represented by Whipplei and its
variety, appear to have undergone a greater adaptation
to general pollinators than the true Yuccas. Retaining
the stylar canal and septal glands of the prototype,
they have acquired a capitate stigma through the
consolidation of the spreading lobes, the small stio1-
matic papillae of other species becoming lengthened as a
means of catching pollen adhering to visiting insects. On
a few pistils, one of which is represented in the appended
figure, the stigma is, in fact, separated into its carpellary

DIALYSIS OF HK8PEROYUCCA STIGMA, X 2.

segments, each of which is strongly revolute. Similar
instances of dialysis have also been observed in the true
Yuccas, and these teratological specimens represent pretty
nearly what I suppose to have been the original form of
stigma in the ancestors of the Yuccas. The pollen grains
may be assumed to have become somewhat viscid as a means
of surer attachment to visitors which did not go deliber-
ately to the anthers, and I am inclined to look on their
agglutination into crude pollinia as a result of this, — per-
haps intensified on the return of the plant to exclusive Pro-
nuba pollination, — rather than an original provision for
their bodily removal by other pollinators. These plants may,
therefore, have branched off from the earlier Yuccas after a
certain dependence on Pronuba had been formed, perhaps

222 MISSOURI BOTANICAL GARDEN.

acquiring their more general adaptations because of separa-
tion from Prodoxids, and readjusting themselves to their
former pollinators on again coming within their reach ; and
I am disposed to think that this is the case, rather than to
assume that the generalization antedates their first asso-
ciation with Pronuba.

The evolution of the Pronubas has presumably gone hand
in hand with the adaptation of the Yuccas to their services
in pollination, and has been sketched, in its essential feat-
ures, by Professor Eiley. It is interesting to observe that
one species, P. yuccasella, accompanies the true Yuccas of
the most differentiated type across the continent from the
south Atlantic states to southern California (and undoubt-
edly the peninsula), and that, as the pollinator of Y. baccata,
it occurs in California associated with P. synlhetica and P.
maculata and its curious black derivative, which pollinate
respectively the archetypal Y. brevifolia and the greatly
differentiated Hesperoyuccas, thus strengthening the in-
ference that the latter two are primarily Pacific types, while
baccata in its present form is an immigrant from the East,
which has been accompanied by the common pollinator of
the eastern species.

In a paper read before the American Association for the
Advancement of Science at Rochester, in August, 1892,
Professor Smith has shown that the curious tentacles used
by the moth in pollinating the Yucca flowers, occupy a
position similar to that of the palpif er on the maxillse of
other groups of insects, and so is disposed to homologize
them with those parts. As Professor Cope has suggested
to me, a fuller knowledge of the embryology of lepidoptera
may show the general prevalence of similarly situated
processes in the early differentiation of the maxillae, and
thus remove the only valid objection that I see to Professor
Smith's conclusions, the isolated occurrence of these
appendages in the group of lepidoptera. At present they
are known in a developed form only on the females of
Pronuba, and as rudiments on the males of that genus and

FURTHER STUDIES OF YUCCAS. 223

in the related genus Prodoxus. The occurrence of such
rudiments in Prodoxus, however, is very interesting from
an evolutionary stand-point, for it points to the inference
that these moths are retrogressions from the Pronubas,
rather than a nearer approach to the common parents of
both.

The three types of fruit on which the primary classifica-
tion of the true Yuccas rests, correspond with three modes
of dissemination in the genus. About half of the recog-
nized species have sweet, edible, pulpy fruits; two have in-
dehiscent fruits similar to the preceding during their early
development, but 'dry at maturity; and the remainder,
including nearly one half of the true Yuccas, and the Hes-
peroyuccas, have dehiscent dry capsules. All of these
fruits agree in their type of structure, as might be ex-
pected from the general uniformity in the parts of the
ovary in the several species. In all of those I have been
able to study during their development, the inner part of
the ovarian wall, corresponding to the superior face of the
infolded carpellary leaves, becomes more or less firm, the
walls of its cells being thickened and deeply pitted, while
the outer part is green and fleshy, and no doubt takes part in
the assimilative work of the plant. In the Sarcoyuccas,
this outer part becomes much thickened and quite succulent
and sweet toward maturity, assuming a yellowish or pur-
plish color and, in short, undergoing the usual ripening
process of baccate fruits. The seeds, meantime, in most of
these species, are immediately surrounded and protected by
the firm inner layer previously mentioned, which suggests in
texture and function the core of an apple, and in which
the seeds rattle with considerable noise when the fruit is
shaken. The pulp is easily removed from this core, which is
usually shaped to the convexity of the thick seeds, so that
when denuded it bears quite a strong superficial resem-
blance to a small ear of corn, a number of interspersed pale
and undeveloped seeds, causing a mottling suggestive of

224

MISSOURI BOTANICAL GARDEN.

the " squaw corn " of the Indians. In aloifolia, where the
pulp becomes almost black throughout, the very slight core
also at length becomes pulpy. These fruits are well adapted
to dissemination by fruit-eating animals, especially birds, the
linn core suggesting that the pulp only is swallowed, the
seeds being thrown away; but I do not know of any
recorded observations on their dissemination.

The Clistoyuccas, with dry indehiscent fruits, comprise
the curious tree Yucca of the deserts, Y. brevifolia, and a
single eastern species, Y. gloriosa. Though frequent in
cultivation, the latter is one of the least known Yuccas, and
its fruit has been observed rarely. All that I can learn of
it points to the conclusion that its fruit is of the Sarcoyucca
type with rather thin seeds and suppressed development of
the exocarp, suggesting a retrogression from aloifolia; but
nothing can be said as to its dissemination. Y. brevifolia,
however, differs from all of the other known species in
having a very thick exocarp, corresponding to the pulp of
the preceding group, but dry and spongy at maturity.
The fruits of this species fall quickly after ripening, either
by a distinct disarticulation or because of the brittleness of
the pericarp at base, and their rounded form and very light
specific gravity render them well developed ' ' tumble
fruits," and point to their dissemination over the dry
sands of the desert by aid of the strong winds which prevail
there, the seeds being liberated ultimately by the breaking
of the fragile pericarp. Although brevifolia appears to be
the least advanced of the Yuccas in its general development,
I am disposed to look on this adaptation of its fruit to
wind dissemination as a special acquisition, rather than
regard it as representing the original type of Yucca fruit ;
yet, so far as the facts are known, it might equally well
be held to be an advance on an earlier unspecialized fruit,
or a retrogression from the baccate type.

In the capsular species, the green exocarp dries down to
a rather thin layer at maturity, and the core, with this
adherent film, dehisces through the true septa, and, for a

FURTHER STUDIES OF YUCCAS. 225

certain distance from the top, through the backs of the
several carpels (PI. 22). The seeds of all of these species
are thin and flat and the capsules are erect, so that the
adaptation to the scattering of the former, a few at a time,
by gusts of wind, is that usual in capsular fruits of this
kind. It is interesting to note that Whipplei and its
variety, representing the aberrant group of Hesperoyuccas,
possess the thin margined seeds of the capsular true
Yuccas, but the capsules dehisce to the base in a loculicidal
manner, that is, through the false partitions, the tough
core-like tissue of which is arranged in a transverse lace-
like structure (PI. 23). Though dissemination depends
on the wind in both cases, the seeds of the capsular true
yuccas are lifted out of the pods by the wind dipping
into the opened top of the cells, while in Hesperoyucca
they are removed by puffs of air entering at the side through
the lace work across the deep lateral clefts, in the manner
beautifully described for Lilium in an anonymous article in
the Bulletin of the Torrey Botanical Club, i. p. 46, and
well known in the basket fruits of some Aristolochias, etc.

EXPLANATION OF PLATES ILLUSTRATING YUCCAS AND THEIR
POLLINATION.

Plates 1-2, y. Guatemalensis, flowering and fruiting plant at the
Garden.

Plate 3, Y. Schottii, near Benson, Arizona.

Plate 4, Y. australis, near Sierra Blanca, Texas.

Plate 5, Y. australis, — a specimen from the same region, cultivated at
the Garden.

Plates 6-9, Y. brevifolia, about Hesperia, California.

Plate 10, Y. elata, near Benson, Arizona.

Plate 15, r. elata, descending axis, twaand a half years from the seed,
one-half size, — the principal growth made in the season when figured,
(after Engelmann) . — Y. filamentosa, germination, X^«

Plate 16, Hesperoyucca Whipplei, at Summit, California.

Plate 17, H. Whipplei, var. gramimfolia, at Arrowhead Springs, Cal.

Plate 18, Y. aloifolia.— 1, Flower, natural size; 2, pistil and stamens,
X2 ; 3, sections of pistil at points marked by dotted lines, X 2.
Y. Treculeana.—l, flower, natural size (after a drawing by Mrs. H. J-
Webber) ; 5, pistil and cross sections, X2-

226 MISSOURI BOTANICAL GARDEN.

Plate 19, r. Quatemalensis. — 1, Flower, natural size; 2, pistil and
stamens, X2 5 3> sections of pistil at points marked, X2 5 *> f ully grown
but green fruit, natural size; 5, seed, X2-

Plate 20, Y. baccata. — 1, Flower, natural size ; 2, pistil and exceptionally
long stamens, natural size; 3, pistil (the upper part in longitudinal
section), and cross sections, X25 4> enlarging ovary, showing Prouuba
punctures, natural size; 6, cluster of fruits, perforated by escaping
Pronuba larvae (after a photograph taken near San Diego, Cal., by Parker
and Parker), reduced.

Plate 21, Y. brevifolia, — 1, Flower, at time of pollination, natural size;

2, pistil in longitudinal section, and cross sections at points marked, X2;

3, Pronuba synthetica, X3 5 *> oviposition of moth, natural size ; 5, head
of laden $?, X*0; 6, young larvae in developing fruit, reduced one-half;
7, ripened but rather small fruit, from which the larvae have escaped,
natural size.

Plate 22, Y. filamentosa.—l, Flower, natural size. r. elata.—2, pistil
and stamens, and cross sections of pistil, X2 ; 3, dehiscent capsule, per-
forated by escaping larvae, natural size. Y. glauca, var. stricta.— 4, pistil
and stamens, and cross sections of pistil, X2« 6> Pronuba yuccasella,
X3.

Plate 23, Pronuba maculata, var. aterrima. — 1, Laden 9, X3; 2> nead
of same, X10- Pronuba maculata. — 3, laden £, X3> aQd venation of
wings ; 4, pollination. Hesperoyucca Whipplei. — 5, flower, natural size ;
6, longitudinal section of pistil, and cross sections at points marked,
X2 ; 7, stamen, adnate to base of petal, X2 > 8, section of ovary punc-
tured in oviposition, X2 > 9, small capsule, dehiscent through the false
septa, natural size.

Unless otherwise stated, the plates were drawn by Miss Johnson, from
photographs or studies by the author, or are reproductions of photographs.

Since the preceding pages were electrotyped, the paper by Professor J.
B. Smith, on the maxillary tentacles of Pronuba, referred to on p. 222,
has been printed in Insect Life, v. 161, Jan. 1893.

PRESS OF Nixon-Jonas PEWTIMO Co., 215 PINK STREET, ST. Louis, Mo.

PLATE l.

YUCCA GUATKMALEXSIS.

KEPT.' Mo. HOT. GAKD., 1893.

YUCCA GUATEXIALEXS1S.

Private lib iry of
J.ELIOT CO1T
Please return.

KEPT. Mo. EOT. GARD., 1S93.

YUCCA SCFIOTTII.

KEPT. Mo. Box. GARD.,

PLATS t.

YUCCA AUSTIIALLS.

KEPT. Mo. Box. CARD.,

YUCC.V AUSTRALIS.

KEPT. Mo. HOT. GARD

PLATE 6.

YUCCA BREVIFOLIA.

REFT. Mo. EOT. GARD., 1893.

YUCCA BltEVIFOLIA.

KEPT. Mo. Box. GARD.,

YUCCA BREVI FOLIA.

REFT. Mo. Box. GARD., 1833.

REPT. Mo. Box. GAUD.

PLATE 10.

YUCCA KLATA.

REFT. Mo. EOT. CARD., 1893.

PLATE 15.

YUCCA ELATA AND FILAMENTO8A.

Private library of
J.ELIOT CO IT
Please return.

KEPT. Mo. Box. <iARD., 1893.

PLATE i<;.

HESPEUOYUCCA WHIPI'LEI.

UEPT. Mo. HOT. GAKD., 18»3.

PLATE 17.

HESPKKOYUCCA VV11IPPLKI, VAK. GRAMIMFOLI^.

KEPT. Mo. Box. CARD., 1893.

1M,ATK 1,-

1

YUCCA ALOIFOLIA AND TRKCULEANA.

KELT. Mo. I'.OT. GAUD., 1803.

YUCCA GITATKMALENSI3.

KEPT. Mo. UOT. GARD.

PLATE 20.

YUCCA I5ACCATA.

KEPT. Mo. DOT. GARO., 1893.

YUCCA BREVIFOLIA.

KEPT. Mo. DOT. GARD., 1893.

YUCCA, § CHAENOYUCCA.

KEPT. Mo. HOT. GAKD.,

PLATE -.>:!.

II

HESPEKOYUCCA WHIPI'LEI, AND VAKIKTV.

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