Lemna and
Spirodela require no supply of vitamin B
1 in their illuminated culture. When
Lemna valdiviana and a certain species of the same genus (not yet identified) are heterotrophically cultured in the darkness, they are able to grow normally only in the first stage, but soon after there appear some ill symptoms in new developing individuals. All plants, young and old, die at last. By means of the transplantation in a culture solution containing vitamin B
1, the plants can recover the healthy growth from the B
1-avitaminosis caused in the darkness. If vitamin B
1 is used in the culture solution, the
Lemna plants continue their heterotrophical growth in the darkness for over two years. The B
1-avitaminous plants recover the healthy growth in one or two days, when they are illuminated. The minimum quantity in which vitamin B
1 permits Lemnaceae plants their bare growth in the darkness, is 3×10
-7mg in 100cc. solution, and for their best growth vitamin B
1 is required in the amount 10
-5mg. The aquaous extract from the normal plant bodies of
Lemna developed in the illuminated condition, is available in, stead of vitamin B
1 for the dark culture of other individuals of Lemnaceae. The same things can be applied for the extracts from yeast and malt roots. Vitamin B
1 is indispensable for the growth of Lemnaceae, and the plants produce it for themselvs under the light.
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