Genèse 30:37

And Jakob took to him a rod of flowering poplar, and of almond, and of the plane tree, and peeled in them white peelings to disclose the white which was in the rods.

AND JACOB TOOK HIM STICKS OF POPLAR. As soon as they agreed that his hire would be these colors it was permissible for Jacob to do whatever he could to cause them to give birth in this manner. Perhaps Jacob had made a condition that he may do with them whatever he wants since Laban did not know of the ramifications of this measure, nor did Laban’s shepherds sense anything when they saw the sticks in the gutters once a year during the days of Nisan. For When the flocks were feeble in the days of Tishri, he did not put them in, otherwise not a hoof would have remained for Laban.
Now some commentators say that the first year [Jacob did not make use of these sticks, but] there were born to him many speckled and spotted ones by virtue of G-d’s blessing which the angel showed him. And then he put the sticks in front of those which were his so that they should give birth in their form. This would prevent Laban from saying that their offspring was stolen by Jacob, [as he would have claimed had they given birth to other colored offspring].
This is the meaning of whensoever the stronger flocks became heated, referring to those that had been born to Jacob by way of G-d’s blessing; but when the flocks of Laban were feeble, he put them not in; so that the feebler were Laban’s, for they did not give birth to speckled ones, and the stronger were all Jacob’s, including their offspring, for they gave birth to speckled ones.

מקל לבנה, the reason why the letter ק in the word מקל has the vowel patach instead of the vowel tzeyreh, as we might have expected, is because it is in a construct form to the word לבנה, the tree that this staff was cut from. We encounter a similar construction for the same reason in Leviticus 27,32 where the Torah speaks of Ma-assar bakar instead of ma-asser bakar, “tithe of the cattle.” The word מעשר is in a construct form to the word בקר. We find a similar construction in Jeremiah 6,26 with the expressionמספד תמרורים, as well as in Amos 5,16 and Numbers 18,26 and Numbers 22,27.

לח, not literally, wet, but not dried out.

מחשוף, exposed, visible. Compare the same expression in Ezekiel 4,7, or in Isaiah 52,10 חשף ה' את זרוע קדשו, “the Lord bared His holy arm.”

ויקח, Yaakov did not do this in the first year, but only from the second year on. He did not place the sticks in front of the animals belonging to Lavan, but only in front of those animals which were now his as a result of the young ones born with the agreed upon skin patterns during that year. When he placed the sticks in front of those animals which were his, he did not intend for them to have young ones of a different skin pattern from the one they already had, but only to ensure that all his animals would give birth to young ones bearing the same skin patterns as did their mothers. In other words, he did not deprive Lavan of anything, either directly or indirectly. He acted in a manner which would not allow Lavan even to suspect him of stealing from him. This is the way my father of blessed memory explained these verses in light of the fact that numerous people, reading the story superficially, had expressed surprise that our patriarch Yaakov had been as devious as a superficial reading of the text makes it appear.

לבנה, a tree (poplar) with a white trunk. (before peeling off its bark) He used such a tree in order to produce the desired colour contrasts after peeling the bark partially into the respective shapes to resemble עקוד ונקוד. This could be done only while the saplings were still moist. He also took branches, or sticks that were moist, fresh, as when peeled they would look more whitish. The trees called here לוז and ערמון respectively, are both well known, (plane-tree ad almond tree.)

ויקח לו יעקב מקל לבנה לח, “Yaakov took for himself rods of fresh poplar;” if you were to ask how a righteous person such as Yaakov could play such a trick, the answer this that according to the agreement between him and Lavan the answer is that when the agreement was made Yaakov had told his father-in-law to remove all the sheep of his that had speckled and spotted skin patterns, etc., meaning the young animals, so that he could not be accused later on as these having been stolen by him. This did not include mature animals with those skin patters. Lavan removed all such animals regardless of their age, making it almost impossible for animals that had never shown such skin patterns to bear young ones that did. He was therefore perfectly fair in looking after his own interests, seeing Lavan had made it almost impossible for him to own flocks of his own without resorting to ingenuity; as a matter of fact he did so, with the help of advice from an angel in a dream, as we read in 31,10. In addition, the sage Rabbi Chayim added that careful reading of the text will show that Lavan changed unilaterally the terms of their contract, which had referred only to animals with the skin pattern known as נקודים, whereas he now had added those with skin patterns known as עקודים. This is why Yaakov on his part saw free to do what he did, fulfilling what is written in Samuel II 22,27: עם עקש תתפל, (David speaking) “and with the deceitful people You will find ways to make them cause their own downfall.”