Forel has justly observed that if insects are guided by "a principal directive sense" the rule is always that they associate the impressions of several senses. Capable of attention, endowed with memory, and very apt in learning, they do not act as pure automata, but, "all ready to put their instincts into play (hereditary automatism), these work with precision when sensations" arise to evoke them.

They know above all how to profit by acquired experience. When, in the course of their work, they have been conducted by chance or by their senses either to sugared baits which they covet or to deceptive flowers, they are assisted by the memory of places and of appearances to return to the first and to avoid the second. This explains the assiduity of the Mellifera among the greenish flowers of ivy, of currant, and of the willows, the decided predilection of Andrena florea for the greenish flowers of bryonia which seem odorless to us, and the disdain of the honey-seekers for the false Melissa though its beautiful big flowers are agreeably perfumed. If it is true that it is at least doubtful that anthophilous insects have the preference, which Herman Miiller attributed to them, for flowers of certain colors, one can be assured that this results from a sensorial association and from experience. Kerner contends that the color scarlet is disagreeable to bees, and he offers as proof the fact that they never visit the splendid red flowers of Pelargonium zonale. But Perez has shown that if a little honey is introduced into the corolla of this plant the bees will visit it with per-severence when they once discover the precious food. So they associate the sensations of form and color with the sense of taste, and, ordinarily neglecting the white and red varieties of this species, continue for a time to visit the scarlet flowers even when these no longer contain honey.

It is because he had not studied the faculties of insects that Plateau was led to deny the vexillary role of floral colorations. In a row of simple dahlias, he covered four heads with squares of different colors in which the perforated middle allowed the yellow flowers to be perceived. Then he hid the perforation with a disk of another color. And finally he tried the two experiments with the green leaflets of the wild creeper [vigne-vierge]. Before the operation the flower heads were very frequently visited by different insects (bumblebees, carpenter bees, Vanessas, etc.). They were also visited afterward, but not without hesitation on the part of the visitors.

Forel repeated the same experiment in a basket in which were blooming forty-three differently colored flower heads. With vine leaves, folded.

He Covered completely twenty-eight of these flower heads, leaving thre others intact. Not without trouble the bees abandoned these, but one of them after two hours recognized the stratagem and reached the flower head by following the lower part of the vine leaf. Others followed her example, and soon the covered fl'ower heads were visited as much as the others. Forel says :

Plateau, then, has experimented badly and concluded falsely. The bees still saw his dahlias at first incompletely covered. "When he afterward entirely covered them, but only from above, the bees had already recognized the strategem and still went to the dahlias from sight. Plateau had not counted upon the memory and the attention of the bees.

Associative memory, as a matter of fact, has reached a remarkable development with certain anthophilous insects. I have observed (1904) the workers of our honey-bee in a field where the common brunelle, the cornicled lotus, plantain, and different species of clover showed some colored spots. Although the flora was scant, the honey-seekers frequented only the brunelle and could recognize its upright clusters in which the unflow-ered calyces formed a base of reddish brown and the violet corollas a terminal crown. The insect examined all the clusters, whether they were or were not terminated by flowers. The coloration of the calyces sufficed to attract it, but it took its flight as soon as it recognized the hopelessness of its search. It associated the notion of color with the idea of harvest, and the color of the inflorescences acted solely as its guide in its journeys. More demonstrative still is the following observation. There grow side by side in America an indigenous cotton and its Asiatic varieties. The former has accessory nectar glands on the green leaflets of its involucre, while the latter have none. But the biologist Allard (1911) has stated that the bees "always visited the involucral nectaries," whichever cotton plant they came to, but once upon the Asiatic varieties, they "soon recognized their mistake after having alighted upon a flower, and hastened to abandon it. ' '

Thanks to their associative memory, the bees very soon acquire habits. Buttel-Reepen1 says:

When the hives are in the neighborhood of buckwheat, flight is very active only from the beginning of the morning up to ten o 'clock, after which they rest for almost the remainder of the day; then begin again actively the following morning. We know that buckwheat produces nectar only in the early hours of the morning. When the honey sources stop, the bees go around a little longer and then suspend their useless flight. In spite of the sea of brilliant flowers and its strong perfume, one finds ordinarily during the day after ten o'clock only a very small number of bees in the buckwheat fields.

1 H. von Buttel-Reepen, Sind die Bienen Reflexmaschinen? 1900. (Biol. Centralblatt, v. 20).

The insect has regulated its habits according to the rhythm of the nectaries.