They were also called "Fibre" needles. Alexander Graham Bell used a sharpened bambo sliver as his first phonograph needle. These were patented on November 12, 1907 by Fred D. Hall of the B & H Fibre Company in Chicago. You could buy 1000 needles for $4, significantly more expensive than steel which cost as little as 50 cents for 1000 depending on model. But the math was more complicated.
Steel needles needed to be changed often the damage shown clearly by the whitening of the groove in loud passages. The big advantage was that you could sharpen bamboo needles. Thus they outlasted a steel needle. The downside being that the organic nature of the bamboo softened the sound, and before amplifiers, there was a notable volume loss. Some records, like early aluminum acetates were intended to only be played with the bamboo needles. Steel needles would quickly destroy the soft grooves in the aluminum. Try to remember this was an era where needle tracking was measures in ounces and not grams and that the soft needle was the best answer at the time.
With a fiber needle cutter (like the device pictured above) bamboo blanks were trimmed and re-trimmed to a sharp point. They also needed to be soaked in paraffin to extend their sharpness beyond one use. The B&H Fibre Needle Company advanced the use of bamboo needles with their triangular bamboo blanks. Their marketing was successful enough to make them a legitamate alternative to steel needles. Victor entered the market not with a competative product but by purchasing B&H in 1909. Audiophiles will tell you today to replace a steel needle after 3 plays or risk damage to the 78. The break through with steel needles in the 1920s was tipping them with tungsten which increased their lifespan. Nobody makes bamboo needles today, so only a select few are still out there soaking and trimming their triangular slivers. There is also a small contingent of loyalists that focus on cactus needles a tradition that dates back to cylinder recordings. More here.