Adding multiple sensors is a good way to collect a range of data for analytical purposes, such as; humidity, temperature, CO2, PH level sensors. This also allows for greater control over the subject plant, in our case Arabidopsis. However, this would lead into a problem with memory. Currently the system is run by an Arduino Uno which has Flash Memory 32 KB of which 0.5 KB is used by; bootloader, SRAM 2 KB, EEPROM 1 KB. With the Lux sensor, 80 % of the flash memory is already taken.
In order to store data from the system the Arduino needs a host shield. The ‘Mini Micro 3.3V’ would be suitable and there are plenty of forums online detailing the application of this device. 
With a memory stick attached, the system can record the data every hour. Later this can be downloaded onto a laptop and plotted to show if there are any fluctuations. Unfortunately, this means we have to upgrade the Arduino model, so we have enough memory to store the code for the extra sensors and the USB stick. There are a number of models that have more storage, Arduino Due has 512 KB flash memory and 96 KB SRAM. This is more than enough for our project.
Attributions: Luke Waller, Umar Farooq
1. Ardiuno, 23 Aug 2008; 'https://store.arduino.cc/arduino-pro-mini'