28 TRANSACTIONS OF THE [ Sess, Lxxum. 
of the market-garden plants in cultivation were attacked. 
But the results were not uniform. Turnips and carrots 
were injured ; beetroot, etc., throve when Heterodera was 
present, but languished in its absence. In the latter case, 
in fact, only stunted, immature plants could be raised. 
This fact was at first regarded as a coincidence merely. 
Histological investigation showed, however, that the worm 
had brought about a useful modification of the tissues. 
Vuillemin and Legrain thus regard the association 
“comme une veritable symbiose.” Further, they conclude, 
Heterodera, which in a moist! environment makes such 
havoc among root crops, produces most salutary effects in 
plants grown among arid desert sands. The injured carrots 
and turnips already referred to, at an early stage succeed 
in overcoming the parasite’s beneficent action. Hence in 
their dry surroundings it becomes impossible for them to 
develop succulent tap roots. Heterodera has great resisting 
power to drought, and can lie dormant for a time. It thus 
proves a useful ally of the higher vegetation, “dans un 
milieu dont laridité exclut les symbioses cryptogamiques.” ? 
The external symptom of the presence of Heterodéra 
was a swelling of the root, spindle-shaped in Monocoty- 
ledons, round more or less in Dicotoyledons. Transverse 
sections showed the following state of affairs:—In the 
vicinity of the worm, certain of the elements, both in the 
primary and in the secondary wood, were transformed at an 
early stage into greatly swollen “utricles.”* These bladder- 
hike formations had collenchymatous walls with numerous 
water passages. The original cell had undergone division, 
without apparently formation of cell walls, till each 
“utricle” contained a multinucleated mass of protoplasm 
1 “Dans les serres ou dans les champs des contrées humides.” 
* For in the desert Leguminous plants when sown fail to produce 
mycodomatia on their roots. 
* The value of this modification depended entirely on the environ 
ment. At El Oued the garden soil, to a depth of 50 m., is nothing 
but sand. Twice a day the soil is liberally watered. Thanks to the’ 
structure induced by the parasite’s attack, the plants take up sufficient 
liquid to last them in the interval. Turnips and carrots resist the 
formation of those giant multinucleated cells. The collenchymatous 
“utricle” in their case collapses at an early stage, or it is filled by 
a cell formation in which starch deposits. Thus though the roots may 
survive owing to their fleshy nature, they never become so succulent 
as others in which the attack has been successfully established. 
