PARK AND CEMETERY. 
109 
and then proceeds up the pistil until its 
head reaches the stigma. The stigma of 
the Yucca is a triangular well or tube 
formed by the union of the three upright 
horn-shaped processes of the ovary. Se- 
curing a firm foothold on these processes, 
the moth proceeds to shave all particles of 
the pollen pellet and with its tongue places 
these in the stigmatic well or cavity, forc- 
ing them far down. This done, it backs 
down the pistil and deposits another egg as 
before, but at a different point, and again 
going to the stigma it repeats the process 
of scraping off pollen from its pellet and 
forcing the particles down the cavity. This 
may be repeated until the stigma well is 
entirely filled. Frequently, however, the 
moth removes to another blossom and re- 
peats the interesting performance. Each 
flower is in condition to be fertilized only 
during a brief period of time, since after 
the first evening the hornlike processes of 
the pistil close over the stigmatic chamber 
and thus preclude the possibility of further 
pollination. In the course of about a week 
the egg hatches and the resulting larva 
feeds on the developing ovules which con- 
stitute its only food. When it has reached 
a mature size it burrows a passage to the 
exterior of the capsule and falls, or lets 
itself down by a silk thread, to the ground. 
Here it bores several inches below the sur- 
face and forms a tough silken cocoon in- 
termixed with soil. It remains as a larva, 
or grub, within its cocoon during the fall, 
winter and spring months and transforms 
to the pupa or chrysalis state only a few 
days before emerging as an adult math 
when the Yuccas bloom again in June. 
It has been found that the Yucca flower 
is incapable of fertilizing itself ; moreover, 
it is impossible for the wind to carry pol- 
len from one plant to another. Extensive 
observations by many scientists in different 
parts of the country, since the early dis- 
coveries by Drs. Engelmann and Riley, 
prove that no other insect does this work 
which is so absolutely necessary to the pro- 
duction of seed. The amount of pollen 
placed in the stigma chamber by the Pro- 
r.uba moth is sufficient to fertilize all the 
numerous ovules of that flower, while each 
larva hatched from the eggs deposited eats 
but comparatively few ovules — only ten or 
a dozen — thus allowing a vast majority of 
them to mature. Were it not for the in- 
tervention of the moth the Yucca plant 
could never reproduce itself except by 
offshoots or an accidental division of the 
parent plant. The plant depends entirely 
on the little moth to aid it in the natural 
method of reproduction. On the other 
hand, this moth does not associate with 
the flowers and fruits of any other plant 
than the Yucca. It feeds during its larval 
or “worn” stage only and then wholly upon 
the seeds of Yucca developing within the 
fruit of the plant. Should the adult moth 
deposit its eggs in the ovary and then fly 
away, the eggs would hatch, but the young 
larvae would soon perish from lack of food. 
To meet this demand the moth has devel- 
oped a form of instinct which impels it to 
place pollen in the stigma of each pistil in 
which it has deposited an egg, insuring by 
this means the fertilization of the ovules 
and consequently a liberal supply of food 
for its offspring. Thus the insect is wholly 
dependent on the Yucca for its existence. 
Through ages of association the plant has 
become adapted to such a degree that it 
cannot be pollinated by any other means in 
nature and at the same time the insect has 
become so adapted that it cannot carry on 
its life history with any other plant. To 
quote from one authority : “The insect 
offers such a remarkable instance of spe- 
cial modification of parts to a particular 
end, and there is such a striking interde- 
pendence between it and its food-plant, 
that Hermann Mueller, who from his ex- 
tensive studies of the relations between 
plants and insects, is most competent to 
speak on the subject, avowed it to be the 
‘most wonderful instance of mutual adap- 
tation’ yet detected.” These are in brief 
the facts that have been brought to light 
and may be observed by anyone who will 
take the time and have the patience to 
watch the snowy little insects on any clear, 
warm ev.ening. 
It is of especial interest to know that 
many of the original observations, both of 
Dr. Engelmann and Dr. Riley, were made 
at the Missouri Botanical Garden through 
the kindness and encouragement of its 
founder, Mr. Shaw. 
CHARACTERISTIC TREES in PHILADELPHIA CEMETERY 
How desolate are the older burial 
grounds, entirely barren of trees, except 
those specimens which have grown wild, 
as compared with our modern park plan 
cemeteries, and how restful and inspiring 
are beautiful groves of judiciously planted 
trees. The lesson of trees was well learned 
years ago at West Laurel Hill, Philadel- 
phia, which has a collection of trees that 
shows the wise conception of the founders 
and subsequent care and training under 
succeeding managers. The care of the 
trees is a paramount issue under an ex- 
perienced and regularly maintained forestry 
department whose duty is to uphold the 
high standard of tree perfection. Every 
tree is considered a valuable asset and no 
labor or expense is spared to guard against 
disease or decay. For the encouragement, 
education and general appreciation of the 
lot holders a tree catalogue is issued, giv- 
ing the common and botanical names, nat- 
ural history and general uses as a product 
of manufacture. Each tree bears a num- 
PLATE NO. 3. 
PLATE NO. 1. 
PLATE NO. 5. 
