268 SUMMARY OF CURRENT RESEARCHES RELATING TO 



this purpose being assisted by the elasticity of the fruit-stalk. The 

 ejection of the nucules in a particular direction is secured by this 

 contrivance. 



Raphides-cells in the Fruit of Vanilla.* — As a general rule, the 

 raphides-cells in the stem and leaves of Monocotyledons are characterized 

 by preserving their division-walls intact. M. L. Guignard has noticed 

 that in the ovary of Vanilla aromatica are cells arranged in rows containing 

 a gummy matter and bundles of crystals of calcium oxalate. The walls 

 which separate these cells from one another have in many cases disappeared 

 owing to their perforation by the raphides. 



Efficiency of the defensive structures of Plants, f — Dr. L. Errera 

 classifies the means of protection of plants against animals under three 

 heads : — (a) biological, {h) anatomical, and (c) chemical. Under the first 

 he places those plants which grow in inaccessible situations, or by their 

 dense growth form impenetrable thickets, or those which owe their exist- 

 ence to protective resemblance. Under tbe second head come spines, 

 prickles, stings, &c., and the various modifications by which plants become 

 hardened, thereby rendering them unfit for animal food. In the third 

 division are the various chemical substances contained by plants, i. e. acids, 

 tannins, essential oils, bitter principles, glucosides, alkaloids, &c. 



The author also classifies plants into those which are sought after, 

 shunned, or neglected by animals. Taking his examples from the Belgian 

 flora, the author gives the percentage of the genera which come under each 

 heading. With coriaceous or scabrous plants, 49 per cent, of the genera 

 are shunned ; with prickly or stinging plants, 35 per cent. ; with plants 

 containing an essential oil, 44 per cent. ; with plants containing a bitter 

 principle, 26 per cent., a glucoside, 28 per cent., and an alkaloid, 9 per 

 cent. The percentage of the genera of those which are sought after is 

 between 35 and 41 ; the remainder being those that are neglected. 



In conclusion the author hopes that this much -neglected branch of 

 botany will not be overlooked in the future, those plants showing protective 

 resemblance being worthy of special study. 



y3. Physiology. J 

 (1) Reproduction. 



Reproductive Organs of Hybrids.§ — The sterility of hybrids is ex- 

 hibited more frequently in the imperfect development of the male than of 

 the female organ. M. L. Guignard has studied the structure of pollen- 

 grains when atrophied through the agency of hybridity. Where the 

 stamens are not converted into staminodes, their arrest of development may 

 be exhibited in various degrees. Very frequently the pollen-grain has 

 only a single nucleus instead of two. The young pollen-grain may then 

 be altogether arrested in its development ; or it may put out a tube which 

 penetrates the stigma, but which has only a germinating and no reproduc- 

 tive power, as in some Begonias. In other cases the pollen-grain — which 

 may even be larger than the ordinary grain — has both its nuclei, but is 

 still destitute of the power of impregnation. In a few cases there are more 

 than two nuclei. 



* Bull. Soc. Bot. France, viii. (1886) pp. 348-50. 



t CE. Soc. R. Bot. Belg., 1886, pp. 86-104. 



X This subdivision contains (1) Keproduction (including the formation of the Embryo 

 and accompanying processes) ; (2) Germination ; (3) Nutrition ; (4) Growth ; (5) Kespi- 

 ration ; (6) Movement ; and (7) Chemical processes (including Fermentation). 



§ Comptes Rendus, ciii. (1886) pp. 769-72. 



