¿Es posible tener dos flow_from_directory en un fit_generator?

Por ejemplo

train_generator_1 = train_datagen.flow_from_directory(
    train_data_dir_1,
    target_size=(img_height, img_width),
    batch_size=batch_size,
    class_mode='binary')

train_generator_2 = train_datagen.flow_from_directory(
    train_data_dir_2,
    target_size=(img_height, img_width),
    batch_size=batch_size,
    class_mode='binary')

custom_vgg_model.fit_generator(
    [train_generator_1, train_generator_2],
    steps_per_epoch=nb_train_samples,
    epochs=epochs,
    validation_data=validation_generator,
    validation_steps=nb_validation_samples,
    callbacks=[checkpointer, csv_logger])