49 
and phosphoric acid in the absorption of food-material, and 
partly in its fixing the oxalic acid, which is even poisonous to the 
plant, and rendering it harmless.’ Connected with this part of the 
subject is the bearing which the study of these crystals may have 
on agriculture. Professor Gulliver has already called attention to 
this point. I was told recently, and shall be glad of information on 
this question, that when a farmer desires to change a grass field 
into a clover field, he simply manures it heavily with lime, without 
necessarily sowing any clover seeds. I thought at the time that 
there was probably some connection between this and the fact that 
the clovers abound in crystals of oxalate of lime. If I am 
correct as to the facts, I believe the explanation to be as follows :— 
We know that the clovers in a healthy state contain vast numbers 
of crystals of oxalate of lime, and that they must therefore secrete 
oxalic acid. Professor Gulliver, indeed, has calculated that one inch 
of the midrib of a leaflet of clover contains 17,500 without counting 
the smaller veins. Ifthe plant cannot get sufficient lime to fix the 
oxalic acid, which Dr. Sachs tells us is poisonous to the plant, it 
naturally remains poor and small, and is easily overpowered by the 
grass ; when, however, it gets the lime it requires, it becomes strong, 
and in its turn overpowers the grass—that is, of course, presuming 
that there is already some clover in the grass field, which is usually 
the case. I may mention also, in support of this view, that crystals 
of lime salts are not found in any grass. It appears to me that we 
learn from this that those plants which, in a healthy state, are 
found to secrete these crystals should be manured accordingly, and 
I think it would be a very interesting experiment to watch the effect 
of different mavures on some plants like the garden-pea, which, as I 
have already said, contains very large numbers of these crystals. It 
seems probable also that the presence or absence of these crystals 
may possibly account for the distribution of some plants. Professor 
Gulliver has said that every British orchid yet examined has been 
found to contain raphides. Now nearly all of our British orchids 
are chalk-loving plants, and indeed they will not exist without it. 
On the other hand, Professor Gulliver informs me that he has also 
found raphides in foreign epiphytal species, while in other epiphytal 
species he has been unable to detect them. Again the dog-mercury 
(mercurialis perennis) abounds in spheraphides, whether growing 
on chalk or not, so that there are many apparent contradictions to 
this view. I think that the subject of manures for plants, and the 
distribution of plants, would form together an interesting study in 
connection with these crystals. My remarks on these two points 
are intended to be regarded rather as suggestions for future investi- 
gations than as established facts. In conclusion, I will, with your 
permission, read one more extract from Professor Gulliver’s pub- 
lished writings on this subject, He says—‘‘ When we consider the 
