My Dear Darwin

My pupil, Rothrock, now away in vacation, has sent me a brief abstract of his Observations on Houstonia cærula.¹ The following are culled from them.

Long-styled: stigmatic hairs are in length —.04 mm.

Short-styled — " " .023"

long

wide Long-styled pollen .020. x .017

Short-styled " .036 x .02 :

in the fresh plants, but dry. Distended with water became round, by increase of the shorter axis alone, the long diameter unaltered.

Long-styled becoming  .026

short-styled "    .036.

(In Mitchella, however, the long diameter was shortened as the other enlarged.)

Pollen of Houstonia not wet, seen endwise is quite strongly 3-lobed. In water the reentering angles come out, and so increase the width.

Short-styled had the smaller stigmas, and the largest and best filled anthers.

The above results I overlooked enough to verify substantially. The following I did not. They may be taken as approximately good

A patch of long-styled—a good deal choked by other vegetation, yielded 34 capsules. The 6 largest of them gave 86 seeds,—average of 14$\frac{1}{3}$. Another patch of same better placed 6 best capsules gave 123 seeds average 21$\frac{1}{2}$.

A patch of short styled: out of 44 capsules, the six best gave gave an average of 15$\frac{1}{2}$ each. Out of the 44, 4 were wholly abortive; 8 averaged 2 seeds each. Most of the rest gave about 6 seeds each.

The above was all from wild plants.

Transplanted specimens in the garden.

Long-styled, average no of seeds of best capsules —13

Short-styled —??

Of 13–short-styled pods

11 were wholly sterile

1 had 4 seeds

1 " 8 "

This was from specimens placed far off by themselves, so that they were not likely to be visited by insects which had left long-styled flowers.

Long-styled flowers fertilised artificially by short-styled pollen.: a patch in what proved to be a most unfavorable situation, much dwarfed. But 6 best capsules gave 77 seeds. In flowers of plants covered with fine netting (coarse gauze) a species of Thrips abounded, also a larva of some small beetle—completely dusted with pollen.² In many flowers a species of Podura.

I have been looking at the flowers of Rhexia Virginica (I suppose you have examined no true Rhexia)³

Style declined to lower side of the flower. Stamens with their anthers also declined. The small subapical pore of, latter facing inwards. A little pressure on the base of the anther causes puffs of pollen to be blown out through the pore.

In one flower only have I observed the style change its position, in that it bent over towards the upper side of the flower;—accidental?⁴ A clump in water now 4 days: no stigma has been detected with pollen on it.⁵

As far as I can see, the likeliest way is that an insect approaching the flower from below, and searching the tube of calyx prolonged above the ovary into a cup (where if he finds any nectar he has sharper eyes than I have),—as he knocks his head against the enlarged bases of the anthers, will get puffs of pollen against his body, I should think on the sides of a humble bee &c. or abdomen underneath.— If he approaches the next flower from the front, below, he will brush against the subcapitate stigma.⁶

No Orchid examined since my last, except Gymnadenia tridentata,—on which I have a few obs.— It is a congener of Platanthera dilatata,—with the discs formed in two large shallow saucers occupying the whole breadth of the stigma; and the pollen pockets most readily, detached from the caudicle, some pulling off at a touch. It must be fertilised by a very fine proboscis.⁷

Several more Orchids will soon be sent me by sharp-sighted youngster up in Maine,—to whom I have just sent a copy of your book, to stimulate him.

My latest from you is July 14.⁸ It leaves me in a state of much anxiety for your boy.⁹ I will hope for a better account in your next.

I looked to-day for seeds of the little Houstonia for you—in vain. I told Rothrock to gather or save some & hope he has, but know not.— I am worth little now for any commission,—and—now that I am to set down to systematic work, shall be worth still less to you.

Ever Yours most cordially | Asa Gray